U.S. patent application number 10/153545 was filed with the patent office on 2003-01-02 for method and system for mapping and tracking information from a plurality of remote stations.
This patent application is currently assigned to YOSEF MINTZ. Invention is credited to Fenster, Paul, Mintz, Yosef.
Application Number | 20030001779 10/153545 |
Document ID | / |
Family ID | 27547413 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030001779 |
Kind Code |
A1 |
Mintz, Yosef ; et
al. |
January 2, 2003 |
Method and system for mapping and tracking information from a
plurality of remote stations
Abstract
A method of tracking changes in position of a plurality of
remote stations, each having, the method comprising: (a) assigning
a plurality of transmission slots to each of the remote stations;
(b) determining, by the respective stations, of their positions;
(c) initially transmitting, by the respective stations of their
positions; (d) determining, by the respective stations, of their
positions, relative to the previously determined and transmitted
positions; and (e) subsequently transmitting, by the respective
stations, of the determined relative positions, wherein the slots
themselves indicate the relative determined position and wherein
the determined relative position is indicated by the presence or
absence of a signal in one or more of said plurality of slots.
Inventors: |
Mintz, Yosef; (Petach-Tikva,
IL) ; Fenster, Paul; (Petach-Tikva, IL) |
Correspondence
Address: |
REED SMITH, LLP
ATTN: PATENT RECORDS DEPARTMENT
599 LEXINGTON AVENUE, 29TH FLOOR
NEW YORK
NY
10022-7650
US
|
Assignee: |
YOSEF MINTZ
|
Family ID: |
27547413 |
Appl. No.: |
10/153545 |
Filed: |
May 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10153545 |
May 21, 2002 |
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08836550 |
Aug 22, 1997 |
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6437743 |
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08836550 |
Aug 22, 1997 |
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PCT/US95/13232 |
Oct 18, 1995 |
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08836550 |
Aug 22, 1997 |
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PCT/EP95/01330 |
Apr 10, 1995 |
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PCT/EP95/01330 |
Apr 10, 1995 |
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08232776 |
Apr 25, 1994 |
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08232776 |
Apr 25, 1994 |
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PCT/EP93/03418 |
Dec 6, 1993 |
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Current U.S.
Class: |
342/463 |
Current CPC
Class: |
H04W 64/00 20130101;
H04W 72/04 20130101; G08G 1/127 20130101; H04W 74/04 20130101; G01S
5/0027 20130101; H04W 28/18 20130101; H04W 8/245 20130101 |
Class at
Publication: |
342/463 |
International
Class: |
G01S 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 1994 |
IL |
111502 |
Jun 19, 1995 |
IL |
114219 |
Oct 11, 1995 |
IL |
115579 |
Apr 11, 1994 |
IL |
109291 |
Dec 4, 1992 |
IL |
103976 |
Claims
1. A method of mapping a plurality of remote stations each having a
varying attribute affecting a characteristic value computed
according to a predetermined procedure comprising: (a) assigning a
plurality of transmission slots to each of the remote stations; (b)
determining, by the respective stations, of their characteristic
values; (c) initially broadcasting, by the respective stations, of
their determined characteristic values in said plurality of
transmission slots, said broadcast characteristic value having a
first characteristic value resolution; and (d) subsequently
broadcasting, by the stations, of their respective characteristic
values in said plurality of transmission slots, said subsequent
broadcasting having a finer characteristic value resolution
relative to said previously broadcasted characteristic value having
a first characteristic value resolution.
2. A method of mapping according to claim 1 comprising repeating
(d) with successively finer characteristic value resolutions until
the characteristic value is broadcast with a desired characteristic
value resolution.
3. A method of mapping according to claim 1 or claim 2 wherein the
finer characteristic value resolution is twice as fine as that of
the previous characteristic value resolution.
4. A method of mapping according to claim 1 or claim 2 wherein the
finer characteristic value resolution is less than twice as fine as
that of the first characteristic value resolution.
5. A method of mapping according to claim 1 or claim 2 wherein a
characteristic value mapping space is divided into a fixed number
of portions and wherein said initial broadcast indicates which of
said portions contains the characteristic value.
6. A method of mapping according to claim 5 wherein said initially
broadcast portion is divided into a fixed number of portions of a
smaller size and wherein said subsequent broadcast indicates which
of said portions of smaller size contains the characteristic
value.
7. A method of mapping according to claim 5 wherein an area
somewhat larger than said initially broadcast portion is divided
into a fixed number of portions of a smaller size and wherein said
subsequent broadcast indicates which of said portions of smaller
size contains the characteristic value.
8. A method of mapping according to claim 1 or claim 2 and
including repeating at least one step of broadcasting, at a coarser
characteristic value resolution, when an invalid signal is received
from a remote station.
9. A method of mapping according to claim 1 or claim 2 wherein at
least one step of broadcasting is repeated periodically to reduce
accumulated errors in the characteristic value.
10. A method of mapping according to claim 1 or claim 2 wherein the
characteristic value is the location of a mobile remote
station.
11. A method of mapping according to claim 1 or claim 2 in which a
base station receives the broadcast signals and transmits a data
stream including information regarding the broadcast signals as
received by the base station.
12. A method of mapping according to claim 11 in which the remote
stations receive the transmitted data stream and utilize it to
determine if their signals have been correctly received by the base
station.
13. A method of mapping according to claim 1 or claim 2 in which a
plurality of base stations receive signals broadcast by the remote
stations.
14. A method of mapping according to claim 1 or claim 2 in which
the plurality of remote stations is targeted from a larger number
of remote stations based on a particular criterion.
15. A method of mapping according to claim 14 wherein the
particular criterion is the value of the characteristic value
possessed by the remote station.
16. A method of tracking a characteristic value of a plurality of
remote stations each having a varying attribute affecting the
characteristic value computed according to a predetermined
procedure, comprising: (a) assigning a plurality of transmission
slots to each of the remote stations; (b) determining, by the
respective stations, of their characteristic values locations
relative to a previously determined characteristic values; and (c)
broadcasting, by the respective stations, of their determined
characteristic values in said plurality of transmission slots,
relative to the previously determined characteristic value.
17. A method of tracking according to claim 16, comprising
iteratively repeating (b) and (c) wherein said previously
determined characteristic value is the characteristic value
determined in the previous iteration.
18. A method of tracking according to claim 17 wherein a
characteristic value region surrounding said previously determined
characteristic value is divided into a plurality of contiguous
regions and wherein the relative characteristic value which is
broadcast comprises broadcasting a signal in one or more of the
transmission slots which indicates which of the regions contains
the determined characteristic value.
19. A method of tracking according to claim 18 wherein the extent
of the surrounding regions is established based on an expected
maximum rate of change in the characteristic value of the remote
station.
20. A method of tracking according to claim 18 wherein the extent
of the surrounding regions is established based on the estimated
actual rate of change of the characteristic value of the remote
station.
21. A method of tracking according to claim 20 wherein the remote
station transmits a signal in an additional slot indicating the
resolution level.
22. A method of tracking according to claim 20 wherein the remote
station utilizes one of a plurality of resolution levels depending
on the rate of change of the characteristic value and wherein the
resolution level utilized depends on the history of the broadcasts
of movement of the vehicle.
23. A method of tracking according claim 22 wherein the size of the
resolution element is increased when a remote station broadcasts a
change in value in a given sense for a predetermined number of
consecutive broadcasts.
24. A method of tracking according to claim 22 wherein the size of
the resolution element is decreased when a remote station
broadcasts no change in characteristic value for a predetermined
number of consecutive broadcasts.
25. A method of tracking according to claim 23 wherein the size of
the resolution element is decreased when a remote station
broadcasts no change in characteristic value for a predetermined
number of consecutive broadcasts.
26. A method of tracking according to any of claims 16-25 wherein
the characteristic value is a vector of dimension n, and wherein
(3).sup.n slots are allocated for broadcasting the characteristic
value, n being greater than or equal to 1.
27. A method of tracking according to any of claims 16-25 wherein
the characteristic value is a vector of dimension n, and wherein
2n+1 slots are allocated for broadcasting the characteristic value,
n being greater than or equal to 1.
28. A method of tracking according to any of claims 16-23 wherein
the characteristic value is a vector of dimension n, and wherein
2.sup.n slots are allocated for broadcasting the characteristic
value, n being greater than or equal to 1.
29. A method of tracking according to any of claims 16-23 wherein
the characteristic value is a vector of dimension n, and wherein
n+1 slots are allocated for broadcasting the characteristic value,
n being greater than or equal to 1.
30. A method of tracking according to any of claims 16-23 wherein
the characteristic value is a vector of dimension n which can
increase or decrease, and wherein one slot is allocated for
broadcasting the characteristic value, n being greater than or
equal to 1.
31. A method of tracking according to claim 30 wherein the presence
of a broadcast signal indicates a deviation in one sense from the
previously broadcast characteristic value and the absence of a
broadcast signal indicates a deviation in the opposite sense from
the previously broadcast value.
32. A method of tracking according to any of claims 16-23 wherein
the characteristic value is a vector of dimension n which varies in
only one sense and wherein (2).sup.n slots are allocated for
broadcasting the characteristic value, n being greater than or
equal to 1.
33. A method of tracking according to any of claims 16-23 wherein
the characteristic value is a vector of dimension n which varies in
only one sense and wherein n+1 slots are allocated for broadcasting
the characteristic value, n being greater than or equal to 1.
34. A method of tracking according to any of claims 20-22 wherein
the characteristic value is a vector of dimension n which varies in
only one sense and wherein only one slot is allocated for
broadcasting the characteristic value, n being greater than or
equal to 1.
35. A method of tracking to any of claims 16-25 and including
repeating at least one step of broadcasting, at a coarser
characteristic value resolution, when a valid signal is not
received from a remote station during tracking.
36. A method of tracking according to any of claims 16-25 wherein
at least one step of broadcasting is repeated periodically to
reduce accumulated errors in the characteristic value.
37. A method of tracking according to any of claims 16-25 wherein
the characteristic value is the location of a mobile remote
station.
38. A method of tracking according to any of claims 16-25 in which
a base station receives the broadcast signals and transmits a data
stream including information regarding the broadcast signals as
received by the base station.
39. A method of tracking according to claim 38 in which the remote
stations receive the transmitted data stream and utilize it to
determine if their signals have been correctly received by the base
station.
40. A method of tracking according to any of claims 16-25 including
a plurality of base stations which receive signals broadcast by the
remote stations.
41. A method of tracking according to any of claims 16-25 wherein
the previously determined characteristic value is determined in
accordance with claim 1 or claim 2.
Description
RELATED APPLICATIONS
[0001] This application is a continuation in part of PCT
application PCT/EP95/01330, filed Apr. 10, 1995, which designates
the United States which is a continuation in part of U.S. patent
application Ser. No. 08/232,776, filed Apr. 25, 1994, which is a
continuation in part of PCT application PCT/EP93/03418, filed Dec.
6, 1993 which designates the United States.
FIELD OF THE INVENTION
[0002] This invention relates generally to a method and system for
obtaining information from a plurality of remote stations.
BACKGROUND OF THE INVENTION
[0003] It is a common requirement to target and possibly identify
quickly one or several out of a plurality of participants according
to specific selection criteria.
[0004] It is frequently required to select one or more participants
according to a "priority" or "characteristic value" based on
specified selection criteria for the purpose of allocating a
particular task to the participant or participants having the
highest priority.
[0005] In dispatching systems, for example, for dispatching a taxi
or messenger to a customer at a specified location, it is desirable
that a suitable (and preferably the most suitable) taxi or
messenger be sent to a particular customer. Generally the nearest,
unoccupied taxi which has sufficient accommodation should be
dispatched to the customer. Furthermore, it is desirable that the
allocation be accomplished in the minimum possible time.
[0006] Typical existing dispatching systems include a central
dispatch station having a transmitter and receiver or a transceiver
in each of the participating vehicles for communicating with the
central dispatch station. Typically, a voice request is transmitted
by a dispatcher to each of the participating vehicles, and the
dispatcher decides which of the vehicles is most suited to the task
in hand based on the replies from the vehicles.
[0007] Such a system would be capable of simple implementation if
the selection criteria related to static variables only. Thus, if
the only selection criterion were a taxi's current distance from
the customer and each taxi were stationary, it would merely be
necessary to extract the taxis' locations once, after which it
would be simple to determine which taxi were nearest to the
customer's location. However, in practice, the selection criteria
relate to dynamic variables which, by definition, are changing
constantly and therefore it is necessary continuously to update
each taxi's distance from the customer's location (and/or other
information required to choose a taxi for the given task) or at
least to do so each time a taxi is to be dispatched.
[0008] In some typical prior art systems, this is done by providing
the dispatcher with a periodically updated map that shows the
respective location of each of the taxis. This updating is
accomplished by the periodic transmission of a location message by
each of the taxis via a communication channel. In order to ensure
that the transmitted data can be received quickly and without
corruption, the total spectrum width of the communication system
must be very large.
[0009] In a system described in EP 0389488 job requests are
dispatched by a controller to mobile vehicles which messages
include information about the location of a job. Each vehicle has a
receiver, transmitter and circuitry to compare the requirements of
the job with the status of the vehicle. If the results of the
comparison is that the vehicle is suitable for the job, then it
transmits a message back to the controller volunteering itself for
the job.
[0010] It should also be noted that, even in the specific case of a
taxi or messenger service, distance from the customer location is
by no means the only criterion according to which a task may be
allocated. Thus, it may well be that the nearest messenger or taxi
is already occupied and is therefore not available for performing
the task. Alternatively, the nearest available taxi may not have
sufficient room for carrying all the passengers to whom a taxi must
be sent; or perhaps a particularly bulky load must be carried and
the nearest, available taxi or messenger is inadequate for the
task.
[0011] Yet a further consideration is that it is often preferred to
dispatch to a customer an idle taxi waiting at the taxi rank rather
than go through the process of transmitting a voice message and
awaiting responses from taxis in the field prior to allocating the
task to one of them. In the event that several idle taxis are
waiting at the taxi rank, or where several taxis are reasonably
close to the customer, it is often preferable that the taxi which
has been idle for the longest period of time be selected.
[0012] Furthermore, it may not always be desirable to dispatch the
nearest available taxi to a particular customer location if other
customers, albeit further away, have made prior requests which have
not yet been serviced.
[0013] Even apart from some of the basic limitations of prior art
systems described above, it is often desirable to target and
possibly to identify participants according to several selection
criteria. This is somewhat analogous to performing a database
search by means of key words which can be combined according to the
rules of Boolean or other logic systems. However, database records
are generally static and are stored at a single location. In
contrast to this, the attributes of the participants that are the
subject of the present invention are dynamic and constantly
changing, and cannot be characterized by static data which can be
stored at a single site. Thus, if the dynamic data characterizing
such participants are to be searched at a single site, then the
data must first be downloaded to the site where the search is to be
performed. During the time that such data are downloaded, they may
well change, thereby compromising the accuracy of the search which
is subsequently performed.
[0014] Another application which requires the receiving and
processing of information from a large number of sources is IVHS.
In this application, for example, information on position and speed
from a large number of vehicles is processed in order to obtain
information on road delays. Again, the sending of large amounts of
information requires substantial bandwidths, even though the
vehicles themselves need not be identified.
[0015] Another previously unsolved problem is the tracking or
mapping of the position of large numbers of vehicles. Prior
solutions to this problem required the broadcasting by each vehicle
of an information bearing signal including at least its position.
When large numbers of vehicles are to be tracked, the amount of
information to be transmitted (and the communication overhead
associated with the transmission) is very large and the available
time/bandwidth necessary is either unavailable or if it is
available, such broadband systems are expensive. The alternative of
trading bandwidth for time, results in a system which is too slow
for many uses.
SUMMARY OF THE INVENTION
[0016] It is an object of some aspects of the present invention to
transmit information from a plurality of remote sources without
requiring that each of the transmissions be on a separate
time/frequency channel.
[0017] It is an object of some aspects of the invention to provide
a method of transmitting information from a plurality of remote
stations wherein the information is contained in the presence or
absence of a signal in a particular time and/or frequency slot and
not in the identification of the particular station which transmits
the information, in the transmission of an information bearing
signal by the remote station and/or in how many stations transmit
signals in the slot.
[0018] It is an object of some aspects of the invention to provide
a method and system for determining "priorities" or "characteristic
values" of a plurality of participants in accordance with one or
more selection criteria and targeting those participants, if any,
having the highest priority or the most suitable characteristic
value.
[0019] It is a further object of some aspects of the invention to
provide such a method and system wherein those participants having
the highest priority or the most suitable characteristic value can
be targeted in a short time.
[0020] Yet a further object of some aspects of the invention is to
provide such a method and system wherein at least one of the
targeted participants can be identified in order that a task can be
allocated thereto.
[0021] Yet another object of some aspects of the invention is to
provide an improved system for real time bus routing.
[0022] It is an object of some aspects of the present invention to
provide a method of determining traffic delays in a road network
based on transmissions from a large number of vehicles without
identifying the vehicles and without receiving information
associateable with a particular vehicle.
[0023] It is an object of some aspects of the present invention to
provide a system for almost real time mapping of the positions of
large numbers of moving stations with higher accuracy and with
greater speed than prior art systems.
[0024] As used herein the term "priority" or "characteristic value"
means, in addition to its normal meaning, a characterization
according to a protocol which takes into consideration one or more
elements associated with a person or object being
characterized.
[0025] According to a broad aspect of the invention a call is
broadcast or otherwise transmitted to a plurality of remote
stations. Each of the plurality of stations determines a
characteristic value or priority based on certain predetermined
attributes of the station and broadcasts or transmits an indication
signal during a communication slot which is indicative of the
characteristic value, or preferably of a range of the
characteristic value. In some aspects of the invention, more than
one remote station will broadcast at the same time and frequency
during at least a portion of the process.
[0026] In one embodiment of the invention, all of the stations
broadcast or transmit at the same frequency, i.e. all of the slots
have the same frequency and the time of the slot is determined by
the range of characteristic values. In a second embodiment of the
invention, more than one frequency is used for communication and
both the time and frequency indicate the characteristic value. In a
third embodiment of the invention, all of the stations transmit at
the same time, and the characteristic value is indicated by the
frequency of transmission only.
[0027] It should be understood that since more than one indication
signal may be broadcast or transmitted at the same time and
frequency, there is no identification of the responding stations,
but only an indication of the characteristics (or rather ranges of
characteristics, since each time/frequency "slot" generally
represent a range of characteristic values) which characterizes at
least one remote responding station.
[0028] It should also be understood that in many preferred
embodiments of the invention, the transmitted information signals
are "non-information bearing signals" in that the signals per se
carry no information, only the slot in which the signal occurs
carries information. Information about the identity of the
transmuting station may not be of present interest or
alternatively, in some applications, certain slots are used only by
a given remote station, whereby the broadcasting station may be
identified.
[0029] According to one aspect of the invention the characteristics
are one or more priorities associated with the stations.
[0030] In one aspect of the invention a control center monitors the
transmissions of the remote stations and determines which of the
slots having an indication signal has the highest priority. It is
convenient to order the response time period into time (or
time/frequency) slots each representing a range of priority values
preferably in descending order of priorities. Thus, the control
center need only look for the earliest slot which contains an
indication signal.
[0031] Having determined the highest range of priorities which are
held by at least one remote station, a second call is preferably
broadcast or otherwise transmitted asking for responses only from
those remote units within this range. The time or time/frequency
slots are now distributed, either by a predetermined protocol or
specifically by the particular call, so as to cover this range of
priority values.
[0032] The stations which have priorities within this range
broadcast or otherwise transmit indication signals in response to
the new call in the predetermined time or time/frequency slots.
This process of determining the highest range of priorities and
redividing the range continues until a given criteria is met. This
stage of the process often termed herein the "targeting phase,"
(sometimes referred to herein as the "first phase" or "phase one")
ends when the priority range ceases to be significant or the number
of sub-ranges which are filled falls below a predetermined number
based on the statistics of the total number of participating remote
stations and the final range or priorities or where some other
predetermined criteria is reached. At this point the number of
station which are responding to the highest priority is believed to
be small.
[0033] Before going on to the next stage it may be useful to
estimate the number of stations which have responded to the highest
priority. One method of making the estimate is by analysis of the
data from the final step of phase one. A more accurate method of
estimating the number of stations having the highest priority is to
request each of these stations to transmit an indication signal at
a randomly chosen slot over at least a portion of the entire range
of time and frequency slots. Since the number of slots is now
expected to be large compared to the number of stations, the number
of slots which have signals is a good indication of the number of
stations. An estimate of the actual number of responders is then
based on the statistical relationship between the actual number of
responders and the number of slots in which a signal is broadcast.
If fewer stations are expected, only a single time slot may be used
and only the frequency is chosen randomly by the stations.
[0034] The system then preferably initiates an "identification
phase" (sometimes referred to herein as "second phase" or "phase
two") starting with the broadcast or other transmission of an
additional call requesting those stations within the highest
(final) range of priorities found in the targeting phase to
identify themselves. Each of the stations having a priority in this
range broadcasts or otherwise transmits a signal including an
identifier of the station or some other message at a slot which it
chooses, preferably at random, from one of a plurality of such
available slots. If only one station is expected to be within the
range of priority values, then only one identification slot may be
allocated. Other types of slots can also be used for the
identification stage, such as coded spread spectrum signals, FDMA
or CDMA. Additionally, multiple slots may be used for the same
priority range to improve the reliability of detection in both the
targeting and identification stages. The identification slots
generally have an information carrying capacity which is larger
than the slots used for indicating priorities since information
(and not only an indication of the presence of a signal) is
transmitted during the identification phase.
[0035] Since, when a plurality of remote stations are within the
final range of values, it can be expected that more than one of the
stations will respond in at least some of the slots, in which case
their identification signal may be unintelligible. However, since
the number of stations is relatively small, at least some of the
slots will have only one identification signal. In general, the
station having this signal is chosen since at this stage the
difference in priority between the stations is generally
unimportant. In some applications more than one identification
signal may be broadcast in a particular slot, however, one signal
may be clear. This station will then be chosen.
[0036] Alternatively, the stations which are left at this stage may
be identified by assigning to each of the remote stations
(including those which are no longer left, since the system has no
indication of those which are left) a slot which is associated with
only one remote station. All of the stations which are left after
the previous stage are invited to broadcast in their identification
slots. One or more of these responding stations is then chosen.
Using this system of identification of the remote stations frees
them of the need to transmit any information bearing signal,
simplifying the system.
[0037] In another aspect of the invention the indication signal
depends on the average velocity or delay of the remote station,
which are generally vehicles. Systems which operate according to
this aspect of the invention preferably broadcast a call to the
remote stations which requests those stations having a delay above
a given value or an average velocity below a given value to
broadcast a signal indicative of their position. Such signals are
then used to generate a map of those regions for which traffic is
delayed or otherwise moving slowly.
[0038] Preferably, an additional call is sent to the vehicles
requesting transmission of indication signals which position the
slow moving or delayed vehicles at a higher resolution than that of
the first call. Further calls may be made to allow for transmission
of additional information on the status of the vehicles to provide
further characterization of the delays.
[0039] In a preferred embodiment of the invention optimum routing
of buses is made based on their positions along the route. In
accordance with this embodiment, information on bus positions along
the bus line is transmitted to a central dispatch station which
calculates a new optimized schedule based on these updated
situation reports. It should be understood that, while in general
position is a two dimensional vector, the position of the bus along
its route can be given by a single variable.
[0040] In a further preferred embodiment of the invention the
position of a large number of vehicles can be mapped and tracked in
near real time using a relatively narrow bandwidth. In this
embodiment each vehicle is assigned a number of slots which are
used only by that vehicle.
[0041] The vehicles must first be mapped in a preferred first,
mapping, phase of the mapping and tracking procedure. In the first
step of this phase, the total area of interest is divided into
preferably nine areas, each of which is assigned a slot. The
vehicle broadcasts a signal in the slot which corresponds to its
present position. In a second step of the mapping phase, the area
previously indicated as containing the vehicle is expanded to fill
the nine slots. Alternatively, the area which is zoomed into the
nine slots is slightly larger than the area of the previous
broadcast to avoid a situation in which the vehicle was at the
border of the area and left the area between steps.
[0042] This identification of one area and consequent new zooming
and sub-division is repeated several times until the required
resolution is achieved. The highest practical resolution, as will
become clear below, is the distance that a vehicle could travel in
the time it takes to perform a tracking cycle as described below.
Within five iterations the individual resolution can be improved
from 3.3 km to about 40 m.
[0043] In a, second, tracking phase of the mapping and tracking
procedure, performed periodically after the required resolution is
reached, preferably, nine slots, representing a 3.times.3 area of
resolution areas, are used to track additional movements of the
vehicle. The central one of the nine areas corresponds to the area
occupied by the vehicle at the end of the mapping phase (or during
a previous periodic updating iteration of the tracking phase).
During each periodic update, each vehicle broadcasts in a slot
which corresponds to either its previous position (the slot
corresponding to the center area of the 3.times.3 group of areas)
or one of the adjoining areas. In the next following iteration, the
newly chosen area is the center of the 3.times.3 matrix.
[0044] In a further preferred variation of this embodiment of the
invention, only 5 slots are utilized to map into the 3.times.3
area. One of these slots represents one of the corners (or the
center) of the 3.times.3 area and the other 4 slots represent north
south or east west variations.
[0045] In a further preferred embodiment of the invention, nine
areas are represented by a four bit word which is sufficient to
define the 3.times.3 matrix of elements.
[0046] In general, one or more base stations may be used for
broadcasting calls and/or receiving responses from remote stations.
If more than one base station is used, each station preferably
performs a reduction of the data which it receives by either
choosing its best candidate for performing the task or by
performing a mapping function of its nearby region or of its
associated vehicles. The base stations then preferably send this
reduced information to a central base station which makes the final
decision, constructs the desired map or performs any other final
analysis. Furthermore, the central base station would, in a
preferred embodiment of the invention, instruct each of the base
stations as to which additional queries they should make. In this
situation the subsequent queries need not be the same for all the
base stations.
[0047] There is therefore provided, in accordance with a preferred
embodiment of the invention, a method mapping of the characteristic
values of a plurality of remote stations each having a varying
attribute affecting a characteristic value computed according to a
predetermined procedure comprising:
[0048] (a) assigning a plurality of transmission slots to each of
the remote stations;
[0049] (b) determining, by the respective stations, of their
characteristic values;
[0050] (c) initially broadcasting, by the respective stations, of
their determined characteristic values in said plurality of
transmission slots, said broadcast characteristic value having a
first characteristic value resolution; and
[0051] (d) subsequently broadcasting, by the stations, of their
respective characteristic values in said plurality of transmission
slots, said subsequent broadcasting having a finer characteristic
value resolution relative to said previously broadcasted
characteristic value having a first characteristic value
resolution.
[0052] Preferably, (d) is repeated with successively higher
characteristic value resolution until the characteristic value is
broadcast with a characteristic value resolution. The higher
resolution preferably twice, or somewhat less than twice the first
position resolution.
[0053] In a preferred embodiment of the invention, a mapping space
is divided into a fixed number of portions and wherein said initial
broadcast indicates which of said portions contains the position.
Preferably, the initially broadcast portion or a portion somewhat
larger than the initially broadcast portion is divided into a fixed
number of portions of a smaller size and wherein said subsequent
broadcast indicates which of said portions of smaller size contains
the characteristic value.
[0054] There is further provided in accordance with a preferred
embodiment of the invention, a method of tracking a characteristic
value of a plurality of remote stations each having a varying
attribute affecting the characteristic value computed according to
a predetermined procedure, comprising:
[0055] (a) assigning a plurality of transmission slots to each of
the remote stations;
[0056] (b) determining, by the respective stations, of their
characteristic values relative to a previously determined
characteristic value; and
[0057] (c) broadcasting, by the respective stations, of their
determined characteristic values in said plurality of transmission
slots, relative to the previously determined characteristic
value.
[0058] Preferably the method includes iteratively repeating (b) and
(c) wherein said previously determined characteristic value is the
characteristic value determined in the previous iteration.
Preferably, a characteristic value region surrounding said
previously determined characteristic value is divided into a
plurality of contiguous regions and wherein the relative
characteristic value which is broadcast comprises broadcasting a
signal in one or more of the transmission slots which indicates
which of the regions contains the determined characteristic value.
More preferably, the extent of the surrounding regions is
established based on an expected maximum rate of change of the
characteristic value in the remote station.
[0059] In a preferred embodiment of the invention, the previously
determined characteristic value is determined in accordance with
the mapping method.
[0060] A preferred embodiment of the invention includes repeating
at least one step of broadcasting, at a coarser characteristic
value resolution, when a valid signal is not received from a remote
station during mapping or tracking.
[0061] In a preferred embodiment of the invention at least one step
of broadcasting is repeated periodically to avoid accumulated
errors in tracking or mapping.
[0062] In an especially useful preferred embodiment of the
invention, the characteristic value is the location of a mobile
remote station.
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] In order to better understand the invention and to see how
the same may be carried out in practice, non-limiting preferred
embodiments of the invention will now be described with reference
to the accompanying drawings, in which:
[0064] FIG. 1 shows schematically the principal components of a
preferred system for carrying out a dispatching function in
accordance with one preferred embodiment of the invention;
[0065] FIG. 2 is a flow diagram showing the principal steps
associated with a preferred method of carrying out a dispatching
function in accordance with the preferred embodiment of the
invention;
[0066] FIG. 3 shows schematically how vehicles are targeted during
an initial phase of targeting based on distance from the customer
location in accordance with a preferred embodiment of the invention
for carrying out a dispatching function;
[0067] FIG. 4 shows schematically how vehicles are targeted during
a second iteration of targeting based on distance;
[0068] FIGS. 5A and 5B are two portions of a state diagram showing
various options associated with a first targeting phase according
to a preferred embodiment of the invention for carrying out a
dispatching function;
[0069] FIGS. 6A and 6B are two portions of a state diagram showing
various options associated with a second identification phase
according to a preferred embodiment of the invention for carrying
out a dispatching function;
[0070] FIGS. 7A, and 7B show timing diagrams relating to the
targeting and identification phases respectively of a priority
discrimination according to a preferred embodiment of the invention
for carrying out a dispatching function;
[0071] FIG. 8 is a block diagram showing the principal components
in a control center according to a preferred embodiment of the
invention for carrying out a dispatching function;
[0072] FIG. 9 is a block diagram showing the principal components
of a control unit in respect of each of the remote units in
accordance with a preferred embodiment of the invention for
carrying out a dispatching function;
[0073] FIG. 10 shows an initial map generated in an IVHS system in
accordance with a preferred embodiment of the invention;
[0074] FIG. 11 shows a second, more detailed map, generated during
a second iteration in an IVHS application in accordance with a
preferred embodiment of the invention;
[0075] FIG. 12 shows a graph of additional information which is
generated in an IVHS application in accordance with a preferred
embodiment of the invention;
[0076] FIG. 13 shows a graph of further additional information
which is generated in an IVHS application in accordance with a
preferred embodiment of the invention;
[0077] FIG. 14 is a general block diagram of a transmitter for an
IVHS system in accordance with a preferred embodiment of the
invention;
[0078] FIG. 15 is a block diagram of a receiver for useful for both
IVHS and dispatching systems in accordance with a preferred
embodiment of the invention; and
[0079] FIGS. 16A-16C shows a scheme for slot distribution for
tracking of individual vehicles.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0080] FIG. 1 shows a typical scenario of a dispatch situation in
connection with which the invention may be employed. In this
scenario a geographical area 10 is defined by a boundary 11 within
which a system according to the invention is operational.
[0081] An identification system according to the invention includes
a controller such as a control center (base station) 12 and,
optionally, a plurality of taxi stands 13, 14 and 15 which
constitute sub-control units each of which serves a respective
region within area 10 and which may forward a customer request to
control center 12.
[0082] Associated with each of stands 13, 14 and 15 are respective
groups of participants (e.g. taxis) of which two groups 18 and 19
associated with stands 13 and 15, respectively, are shown in FIG.
1. The groups of participants 18 and 19 generally comprise some
taxis which are stationary proximate their respective stands
awaiting instructions therefrom and other taxis such as 20, 21, 22,
23 and 24 which are circulating within area 10 and are either
available for performing a task on receiving instructions or,
alternatively, are occupied and therefore unavailable.
[0083] A customer 25 located somewhere within area 10 relays a
request for service to control center 12 telephonically via a
Public Switched Telephone Network (PSTN). Control center 12, in
turn, broadcasts an invitation message to all of the participants
in area 10 either directly or via a remote station 30 which is
typically located so as to cover all of area 10. Control center 12
can also receive messages via station 30. Alternatively, control
center 12 broadcasts and receives messages directly.
[0084] Remote station 30 may be located inside area 10, or
alternatively if the area is built up with tall buildings, outside
the boundary of the built-up area, if this siting reduces the
blocking of signals between the taxis and the repeater station by
tall building and the like or for other reasons.
[0085] Sometimes, customer 25 telephones a particular taxi stand
since this is the nearest stand to the customer's location. In this
case it is generally preferable that one of the taxis associated
with the taxi stand be dispatched to the customer unless, of
course, all of the taxis associated with the stand are currently
occupied (or otherwise unsuitable), in which case one of the taxis
associated with another of the stands will be allocated for the
task.
[0086] In this case, the association of a taxi with a particular
stand may constitute at least one of the criteria involved in
choosing the taxi to be allocated to customer 25. Such a selection
criterion is a static variable and, once fixed, never varies
because a taxi is always associated with one stand. However, the
actual priority assigned to each of the taxis is also a function of
several independent dynamic factors which are subject to constant
fluctuation. Of these, the taxi's distance from the customer is the
most important example. However, other dynamic conditions
pertaining to a taxi's instantaneous status also affect the
respective priority of the taxi so that, for example, a taxi which
is currently occupied or one which has insufficient occupancy for
the number of passengers to be collected would not participate in
the selection process and a taxi which is waiting at a stand would
get priority. The idle time of the taxi can also be an important
criteria.
[0087] It will be appreciated that in general there are many
different contributory factors, or selection criteria, which
influence the priority assigned to each individual taxi within area
10. Moreover, it is generally the case that each selection
criterion has a different "weight" associated therewith so that the
final magnitude of the priority associated with each respective
taxi is built up from many different selection criteria each of
which exert a different influence on the actual priority
assigned.
[0088] For example, in the simplest case, it may be that only
distance from the taxi to customer 25 is of concern. Such a simple
case would not take into consideration the fact that other
customers may already have requested service and may not yet have
been processed. Thus, another customer near customer 25 but still
somewhat further away from the nearest available taxi in area 10,
may have a prior claim for service. However, in the simplest of
systems where only distance from the taxi to the customer is
important, such a prior claim would not be recognized.
[0089] In a preferred system where many factors are taken into
account the priority assigned to each taxi may often be viewed as a
multi-dimensional vector which is the vector sum of component
priority vectors each relating to a different selection
criterion.
[0090] A preferred method for allocating a task to one of the taxis
in response to a request by customer 25 will now be explained with
reference to FIGS. 2 to 7. For the sake of simplicity of
presentation only, it will initially be assumed that the only
selection criterion of interest is the distance of a taxi from
customer 25.
[0091] FIG. 2, shows a flow diagram of the operation of a preferred
system of the invention. The left portion of the flow diagram
comprises operation of a first, targeting, phase and the right
portion of the flow diagram comprises operation of a second,
identification phase. The targeting phase starts with the
broadcasting of a call message to all of the participating taxis
informing them that a priority must be determined for responding to
a pending request for service. The criteria for determining the
priority may be sent together with the call or, alternatively, may
be part of a preset protocol used for all such determinations.
Alternatively, there may be several such protocols one of which the
call identifies by a code. In the very simple case of a dispatching
system wherein distance of a taxi from a specified location is the
only selection criterion, there is no need to inform the taxi of
the selection criterion each time an invitation message is
transmitted.
[0092] Responsive to the call, each of the taxis uses the selection
criteria to determine its own priority in accordance with the
protocol. The protocol also includes a plurality of ranges of
priority values and a communication protocol which subdivides a
time period and/or a frequency range into a plurality of time or
time/frequency slots each of which is associated with one of the
ranges of priorities.
[0093] Each of the participants who is not immediately eliminated
from further participation owing to gross unsuitability (e.g., they
are already occupied or is already responding to a call) responds
to the call message by transmitting an indication signal in the
appropriate time or time/frequency slot in accordance with his
respective priority. The indication time slots all start at a time
relative to a time base common to all of the participants. It is
important to note that for this embodiment of the invention all
those responding participants having a priority within the same
range respond at the same time and frequency. As a result,
substantially simultaneous indication signals are received by the
control center from those participants having the highest priority
as determined at the current priority resolution according to the
protocol. The indication signals, which are preferably pulsed CW
(i.e., they are pulsed signals at a particular frequency having no
information content other than that given by the time at which the
transmission occurs and the frequency of the transmission), are
sufficiently non-destructive with respect to other simultaneously
transmitted indication signals and have at least sufficient pulse
width so as to permit an indication that at least one of the taxis
has responded in a given time slot. In certain cases it may be
necessary to add some dithering or other variations to the signals
so as to avoid destructive interference between the signals.
[0094] Since the indication signals may, and typically do, overlap,
even a fairly narrow bandwidth broadcast channel may be employed,
there being no requirement to discriminate between different
indication signals in the same priority slot. Furthermore,
intermodulation effects between the indication signals in a given
slot are not important, since only the presence of at least one
indication is required, and the intermodulation does not affect
this determination.
[0095] The control center monitors any response and determines
which slots have a true indicator signal (as opposed to noise or
other transients). Preferably, the time slots are arranged in
descending order of priorities, such that the control center may
ignore all slots after the first one (or some other small number
of) "occupied" slot.
[0096] The control center targets all those responding taxis having
the highest priority range in respect of which a valid indication
signal has been received. Except as will be described below, taxis
having a lower priority are excluded from further
consideration.
[0097] If a predetermined criteria for stopping the targeting phase
has not been reached, then an additional call is broadcast
requesting all those taxis which have a priority within the highest
priority range to respond. The response of the taxis is similar to
that sent in the previous step except that the time or
time/frequency slots now represent sub-ranges within the highest
indicated priority range or ranges. In general the call will
include this range and may include an indication of the protocol
for dividing the slots among the priorities.
[0098] It should be understood that, for the more general case of
multiple criteria, the priority vector may be a function of the
iteration number and/or the priority range. Thus for example, the
first iteration may be used to eliminate taxis which are far away
from the destination without giving much weight to the idle
(waiting) time. The second iteration may give a greater weight to
the idle time or to other factors. In general, taxis which have
moved closer to the destination since the last call and have an
increased priority may participate in the second iteration even if
they did not have the highest priority in the previous iteration or
were not detected as having this priority. Furthermore, a special
slot (hereinafter also referred to as a "miss" trap) may be
provided for taxis whose priority is now higher than the highest
range detected in the previous iteration. These taxis would take
precedence over the other taxis by using the special slot.
[0099] This iterative reduction of the number of participants
continues until a predetermined criteria is reached. This criteria
may include consideration of the priority resolution achieved. The
criteria may include a statistical estimate of the number of
vehicles which have not been eliminated. For example, if in a given
iteration in which a substantial number of sub-slots have been
allocated, only one or a few sub-slots contain a response, it is
then fairly certain that the number of taxis left in the system is
small (or even one) and the iteration process (and the targeting
phase) is ended.
[0100] Another iterative approach which may sometimes be used is to
restrict the responders in the first phase to a single range or a
limited number of ranges. Assuming that the range of interest is
between 0-10 km from the customer. A first call would only ask for
responses from those taxis which are closer than 5 km from the
customer. This distance could be divided into ranges or a single
range could be used. If there were no responses, then the call
would request responses from those taxis in the range of 5-10 km.
If there were a response, then further delineation of the range
would successively narrow the range of distances. In this method of
restriction all positive responses to the query are preferably
broadcast in the same time/frequency slot.
[0101] Preferably, in the targeting phase no participants are
actually identified, and therefore it is not yet possible for the
control center to dispatch a particular taxi to the customer.
Before this can be done, it is first necessary to complete a
second, identification, phase wherein one of the taxis targeted at
the end of the first phase is uniquely identified.
[0102] An additional call is broadcast or otherwise transmitted to
the participants indicating that an identification phase is to
begin. All of the targeted participants remaining at the end of the
first phase are invited to broadcast or otherwise transmit their
identification codes in one of a number of identification slots
(which may be time or time/frequency slots, DS-CDMA or FDMA slots).
These slots have a duration (or information bandwidth) commensurate
with the information to be transmitted by the taxis. The number of
identification time slots is determined in accordance with the
protocol and is application-dependent, and may be based on the
number of participants which are believed to be (or estimated to
be) left.
[0103] For example, in a dispatching system, the priority scale may
extend from a distance of 10 km from the customer location and the
initial priority resolution (so far as the distance criterion is
concerned) may be 1 km which is reduced during two successive
iterations to 100 m and finally to 1 m. At such a fine priority
resolution it is not to be expected that more than a small number
of taxis will be targeted so a fast converging identification phase
having only a few time slots ought to be sufficient for identifying
one of the targeted participants. It is not suggested that a 1 m
distance is significant in determining priorities for taxis,
however use of such fine distinctions aids in reducing the number
of taxis which participate in the identification phase. However, as
will be explained below, the protocol has built therein sufficient
discrimination to allow for possible errors in the number of
identification time slots allocated and to compensate for such
errors as required.
[0104] The identification slots are preferably not assigned in any
way, and the taxis choose their slots in some random way. It can be
expected that at for least some of the slots more than one taxi
will broadcast its identification information. Such broadcasts
probably can not be read by the control center which will choose
the first taxi which it can identify. If multiple dispatches are
required to the same destination, as for example where there are
too many passengers for one taxi, the second phase may have to be
repeated several times until the required number of taxis are
dispatched. Furthermore, in extreme cases, it may be necessary to
call for identification from taxis having a lower priority.
[0105] As in the targeting phase, a slot may be provided in the
identification phase for taxis having a higher priority than the
call. These taxis may have moved closer to the destination or their
signal may not have been received by the receiver due to
interference or blockage.
[0106] Alternatively, the stations may be identified in an
alternative embodiment of the identification phase in which a slot
is assigned to each of the remote stations (including those which
are not targeted, since the system has no indication of those which
are left). All of the stations which are targeted are invited to
broadcast in their identification slot. One or more of these
responding stations is then chosen. Using this system of
identification of the remote stations frees them of the need to
transmit any information bearing signal, simplifying the
system.
[0107] Having described the overall method for iteratively
targeting, during a first phase, successively fewer participants
and then, during a second phase, identifying a desired number of
the targeted participants, there will now be described a specific
application thereof to the scenario depicted in FIG. 1 and with
reference to FIGS. 3 to 7 of the drawings.
[0108] Referring then to FIG. 3, a customer 25 has requested a
taxi. Shown within a circular target area 40 centered about
customer 25 and having a boundary 35 at different distances from
customer 25 are four taxi vehicles designated as V.sub.a, V.sub.b,
V.sub.c, and V.sub.d. Vehicles outside boundary 35 are excluded
from consideration.
[0109] Target area 40 is split into a plurality of concentric
sectors of which only the outermost sectors 42, 43, 44 and 45 are
shown each having a width .DELTA.R and being radially disposed with
respect to the customer. Adjacent sectors 42 and 43 or 43 and 44 or
44 and 45 are contiguous although for the sake of clarity and
explanation they are shown in FIG. 3 as separated from each
other.
[0110] It will be noted that vehicles V.sub.b and V.sub.c are
within the first (innermost) sector 42, vehicle V.sub.d is within
the middle sector 44 and vehicle V.sub.a is in the last (outermost)
sector 45. Since it is desired to allocate the task of servicing
the customer to the vehicle which is closest to him, it is clear
that one of the two vehicles V.sub.b and V.sub.c in the innermost
sector 42 must be identified as the most suitable for the task. It
will also be apparent that the number of vehicles which exist in
any particular sector is a function of the width of the sector.
Thus, if the width of each sector is increased from .DELTA.R to
3.DELTA.R, it is apparent that vehicles V.sub.b, V.sub.c and
V.sub.d will now exist in the new, innermost sector comprising
original sectors 42-44. In this manner, the width of each sector
.DELTA.R constitutes a priority resolution with which a priority is
assigned to the participating vehicles. The coarser (i.e. lower)
the resolution, the more vehicles will answer the selection
criteria and be rated at a particular priority associated therewith
while the finer (i.e. higher) the resolution, the smaller the
number of vehicles which answer the selection criteria and are
rated with the corresponding priority.
[0111] Thus, after a first step of targeting in which a small group
of taxis is chosen, in a second step of targeting the highest
priority taxi, a coarse resolution (finer however than that in the
first step) is set as shown in FIG. 3 and a call message is
transmitted by control center 12 to all of the participants. The
call message also preferably defines a time interval .DELTA.T which
is divided into an equal number of time slots .DELTA.t generally of
equal width such that the total number of time slots is equal to
the total number of priorities: i.e. the number of sectors. In a
further preferred embodiment of the invention, frequency diversity
can be used to define multiple slots at the same time, each of the
slots being at a different frequency distinguishable by the control
center.
[0112] Upon receiving the call message, each of the participating
taxis determines its priority in accordance with the selection
criteria, which, in the simplest case, is assumed to be solely the
distance of the participant from the customer and within the
maximum radius R.sub.max. Thus, vehicles V.sub.b and V.sub.c are
both assigned the highest priority, while vehicles V.sub.d and
V.sub.a n that order) are assigned successively lower priorities.
It should be noted that typically there may be hundreds of vehicles
in the target area 40; only a few are shown in the figure for the
sake of clarity. Further, each vehicle may have a handset (see FIG.
9) having a disabling switch by means of which the driver can
prevent the transmission of a response message upon receiving an
call message from control center 12. By such means he can go off
duty, etc.
[0113] The active participants V.sub.a to V.sub.d now transmit an
indication signal within the time slot .DELTA.t corresponding to
their priority. Thus, vehicles V.sub.b and V.sub.c transmit an
indication signal first; vehicle V.sub.d transmits his indication
signal second; and vehicle V.sub.a transmits his indication signal
third. In an actual situation, of course, there may exist many time
slots corresponding to a large number of coarse resolution
priorities and perhaps hundreds of vehicles will transmit an
indication signal in the same time slot. This, in itself, is not
important because all that matters during this first phase of the
process is to determine the first time slot (or more generally, the
slot representing the highest priority) in which a vehicle
transmits an indication signal.
[0114] This having been done, it is immediately clear which is the
nearest sector to the customer in which at least one vehicle is
located and therefore all of the vehicles in all of the other
sectors may now be eliminated. In a practical implementation of
such a system, the broadcast and receive time for transmitting the
call message from the control center to the participants and
receiving the first indication signal therefrom takes a short time.
Thus, in a relatively short time interval thousands of participants
in the field can be reduced to a small number of potentially
suitable participants for the task, without the use of excessive
frequency spectrum.
[0115] Furthermore, if a full duplex communication system is used,
the control center need not wait for the entire time .DELTA.T, and
can go on to the next iteration or the next phase immediately when
a first indication signal is received.
[0116] As explained above, this process is repeated iteratively as
often as required, each iteration having successively finer
priority resolutions (i.e. sectors of successively decreasing width
.DELTA.R), until a predetermined resolution is reached. At this
point, the width of the remaining sector is sufficiently small that
only a small number of participants are likely to be found therein.
It is, of course, not known how many participants there are in this
remaining sector since regardless of whether only one participant
or many send an indication signal in a particular time/frequency
slot, the control center does not receive a message which is
capable of uniquely identifying any one of those participants.
[0117] It should be noted that the receive time taken for the
control center to process a response from the highest priority
participants is a function of the number of time slots .DELTA.t.
Thus, as the resolution is increased, there will be more time slots
and, since each requires a minimum transmit time, it might take
longer to identify the highest priority time slot. There is
therefore a tradeoff between, on the one hand, increasing the
resolution so as to identify the most suitable participant in fewer
iterations and, on the other hand, increasing the cycle time of a
given iteration by doing so. The choice of initial resolution and
rate of increasing the resolution may be made based on the number
of participating vehicles and or a priori expectations of the
responses. Thus, the range of values of a priority which are
assigned a given sector may be based on the number of expected
units having that priority. If distance is the sole criteria, the
range of distance values may be proportional to the distance so
that the area of the sectors assigned to each priority may be the
same.
[0118] FIG. 4 shows a subsequent iteration of the targeting phase
wherein the priority resolution is increased and a further call
signal is transmitted to the participants. The currently targeted
participants V.sub.b or V.sub.c in what is currently the highest
priority sector 42 are assigned new slots according to the finer
priority resolution and again transmit indication signals during
time slots corresponding to their priorities. As a result, it
transpires that V.sub.c has a higher priority than V.sub.b and its
indication signal is therefore transmitted first (or in a slot
corresponding to a high priority, even if such slot is not first).
However, from the perspective of the control center, there is no
way of knowing how many participants exist in what is now the
highest priority sector. All that can be known is that at least one
participant has the priority.
[0119] Thus, while there may still be hundreds of participants in
the targeted sector, it is expected that with the increased
priority resolution only a small number of participants will now be
targeted. One of these is now to be identified to respond to the
request for service. During this second phase of identification,
the control center assigns a new time interval .DELTA.T-ID and
divides this time interval into a number of equal width time slots
.DELTA.t (or time/frequency slots) related to the expected number
of participants in the highest priority sector 42. The expected
number of participants in sector 42 is determined statistically as
a function of the resolution of the sector .DELTA.R and according
to the application or according to the method described below. The
only remaining targeted participant V.sub.c in the highest priority
sector 42 now selects randomly one of the time slots and transmits,
within the randomly selected time slot, an identification message
whereby the sending participant can be uniquely identified.
[0120] In the more general case, where there are still a number of
targeted participants, the control center receives a plurality of
identification messages some of which may, of course, have been
transmitted during the same randomly selected time (or
time/frequency) slot. It is understood that where two signals are
transmitted at the same time and frequency, no information on the
identity of the transmitting participant is obtained in the absence
of a capture effect. However, it is expected that at least one of
the identification messages can be uniquely identified and, in this
case, the task is allocated to a participant which can be
identified. Where possible, of course, in the interest of speed,
the task is allocated to the first uniquely identifiable
participant.
[0121] If it is not possible to identify one of the participants
uniquely, the communication protocol allows for appropriate action
according to each particular situation. Thus, it may be that during
the final iteration in phase one, no participants were targeted.
This itself could be due to several different reasons: for example,
the call message may never have reached the participants or, more
likely, the response of the highest priority participants may not
have been received, possibly having been obstructed by an obstacle
in its path.
[0122] Alternatively, possibly too many participants were targeted
in the final iteration of phase one and an insufficient number of
identification time slots were allocated during phase two. In this
case, identification messages may collide during all of the
identification time slots, rendering it impossible to identify any
one participant. In the more general case where more than one
participant is to be identified, it may also occur that too few
identification messages arrive in phase two owing to an
insufficient number of participants having been targeted in phase
one.
[0123] The various strategies for dealing with each of these
possibilities from the point of view of the control center will now
be described with reference to FIGS. 5-6B which show state diagrams
relating to the targeting and identification phases, respectively.
In both of these diagrams the following terminology is
employed:
1 PHASE-1.x :x.sup.th iteration of phase 1; PHASE-2.x :x.sup.th
iteration of phase 2; IB :Control center's Broadcast Message; RD
:Responders' signal Detection and signal processing; IBPH1.x
:Control Center's x.sup.th Broadcast messages in Phase 1; IBPH2.x
:control center's x.sup.th Broadcast messages in Phase 2;
.DELTA.TRTPH1.x :x.sup.th time interval for Responder's
Transmission activity in Phase 1; .DELTA.TRTPH2.x :x.sup.th time
interval for Responder's Transmission activity in Phase 2; x
:Number of iterations in Phase 1 or 2 (application-dependent); NIP
:Total number of iterations performed in current Phase; Limit1,
Limit2 :Application-dependent maximum number of iterations for
Phases 1 and 2, respectively. n :predetermined number of successful
iterations PS :Priority slot
[0124] Thus, referring to FIGS. 5A and 5B, if during a successive
iteration, no indication signal is received (i.e. a MISS is
detected), the initiator requests at least once that all of the
participants who have not yet been identified transmit a respective
indication signal and this is repeated until an indication signal
is received or for a maximum number of iterations determined in
accordance with the protocol. Thereafter, whilst the resolution is
higher than a minimum resolution determined in accordance with the
protocol (and the iteration process has not been terminated for
some other reason), further priorities having a coarser resolution
are assigned to all of the participants who have not as yet been
identified, or until the resolution reaches the minimum
resolution.
[0125] Another way of checking if a MISS is true is to provide an
additional slot during which all of those stations which should
have broadcast during the designated priority slots will broadcast
again. If no signal is received during this slot, the MISS is
verified.
[0126] Referring to FIGS. 6A and 6B, if during any iteration no
identification message is received by the control center and during
preceding iterations fewer than the desired number of
identification messages were received so as to permit
identification of the respective participants or if invalid data
were received, there is further included the step of the control
center requesting at least once that any currently targeted
participants who have not yet been identified re-transmit their
identification message.
[0127] If fewer than the desired number of valid identification
messages are received so as to permit identification of the
respective participants owing to the occurrence of more than one
identification message arriving in the same identification slot or
to any other reason such as receipt of erroneous data, thereby
rendering it impossible to determine the respective
identifications, the following courses of action may be taken.
[0128] One possibility is for the control center to allocate to all
of the targeted participants still remaining and who have not yet
been identified a greater number of discrete identification time
slots than the number previously allocated, and to invite the
targeted participants who have not yet been identified to transmit
a respective identification message during one of the new
identification time slots. In other words, the number of targeted
participants is maintained but more identification time slots are
allocated so as to increase the probability that the desired number
of valid identification messages will be received by reducing the
probability of collisions. Alternatively, the taxis can be required
to choose a random number which can then be compared to some
reference number to eliminate some of the taxis or which can be
used in changing the priorities of the taxis to eliminate some of
them. Alternatively, an additional criteria may be added to reduce
the number of participants.
[0129] Alternatively, if the protocol allows a maximum priority
resolution, then so long as the current priority resolution is
lower than the maximum priority resolution, phase one can be
repeated as required for a maximum number of iterations determined
in accordance with the protocol at successively finer priority
resolutions, until the maximum resolution is reached in respect of
all of the participants who have not as yet been identified. This
causes fewer participants to be targeted and again reduces the
probability of collisions in phase two when any newly targeted
participants are identified.
[0130] If, on the other hand, during a successive iteration, fewer
than the desired number of valid identification messages are
received so as to permit identification of the respective
participants owing to an insufficient number of participants having
been targeted during preceding iterations, then the opposite must
be done. Thus, so long as the resolution is higher than a minimum
resolution determined in accordance with the protocol, phase one is
repeated as required for a maximum number of iterations determined
in accordance with the protocol at successively coarser priority
resolutions until an indication signal is detected or the minimum
resolution is reached. This process is performed in respect of all
of the participants who have not as yet been identified and, by
targeting participants in phase one who were not previously
targeted, increases the probability that the desired number of
newly targeted participants will subsequently be identified in
phase two.
[0131] If, during phase one, no indication signal is received in
response to a call message, the control center requests at least
once that the participants re-transmit an indication signal. On
receipt of the call message, the participants assign themselves
priorities and transmit respective indication signals during a
corresponding indication time slot. This covers the possibility
that the call message never reached the targeted participants or,
alternatively, that their responses never reached the control
center.
[0132] In all of the above cases, data is stored in respect of any
participants who have already been identified and subsequent
iterations are performed only to identify additional
participants.
[0133] The protocol includes at least one termination condition
whereby further iterations are not performed even if no indication
signal has been received and/or if fewer than the desired number of
participants have been identified. This is necessary to avoid an
infinite loop being executed in the event that, in a particular
application, there are not enough participants who can be
identified.
[0134] FIGS. 7A and 7B show a timing diagram relating to the flow
of information between the control center and the participants
V.sub.a, V.sub.b, V.sub.c and V.sub.d during the example of FIGS. 3
and 4.
[0135] It will be noted that in the initial phase of targeting,
each participant selects a time slot according to his respective
priority, such that participants with the highest priority transmit
first. Consequently, as soon as the control center receives a
response from the participants, the highest priority may be
determined immediately in accordance with which time slot data was
first received. Further iterations may now be effected, as
required, there being no need even to await the responses of lower
priority participants. This results in very rapid convergence of
the targeting phase to the priority range containing the most
suitable participant. This requires a full duplex system. FIGS. 7A
and 7B show the timing diagram for a half duplex system.
[0136] In another embodiment of the invention priorities may be
assigned according to a measured elapsed time since participants
have performed some activity. For example, priorities are assigned
to taxis according to the time they have been idle.
[0137] In a first iteration of phase one, the mutually common
priority scale relates to an elapsed time of say 3 hours and the
priority resolution is say one-half hour. Thus, each interval in
the priority scale corresponds to an elapsed time of one-half
hour.
[0138] In a second iteration of phase one, the mutually common
priority scale relates to an elapsed time of one-half hour and the
priority resolution is 2.5 minutes. Thus, each interval in the
priority scale corresponds to an elapsed time of 2.5 minutes. If
during the first iteration a signal was received in the time slot
of two to two and one-half hours, then the time slots in the second
phase may have a resolution of 2.5 minutes and span the range
between these limits.
[0139] If this is considered to be sufficiently fine so that not
too many participants will have the same priority, the process is
terminated after only two iterations. It is now appropriate to
implement phase two wherein one of the targeted participants is
identified.
[0140] It will be understood that since, during the identification
phase, a participant may be, in effect, selected randomly, it
cannot be assured that the identified participant is actually the
one who has waited the longest. However, it can be said with
certainty that the identified participant has the highest priority
to within the priority resolution (in this case 2.5 minutes).
[0141] If, notwithstanding the above expectation, it becomes
impossible to identify a single participant in phase two owing to
too many participants having been targeted during phase one, then,
as explained above, several options are available. More
identification time slots can be allocated in phase two or,
alternatively, a further iteration in phase one can be performed at
an even finer priority resolution, for example 6 seconds, before
repeating phase two in respect of a smaller number of targeted
participants or one of the other options described above may be
employed.
[0142] In all of the embodiments described above, at least two
phases are required to identify a targeted participant. Thus,
during a first phase, participants are only targeted and are
identified during a subsequent second phase. However, according to
another preferred embodiment of the invention, provision may be
made for identifying a participant during the first phase by
transmitting an identification message as the indication signal.
The identification message can be decoded in the particular
circumstance that only one participant has the highest priority, so
that only one indication signal is transmitted in the highest
priority time slot, and there is a sufficiently long time interval
between receipt of successive indication signals by the control
center to allow decoding of the identification signal before a
lower priority indication signal arrives in a subsequent indication
time slot. Alternatively, the identification time slots are made
long enough so that different slots have minimal or no overlap. In
this particular case, the second phase of identifying the targeted
participants is eliminated. It should be noted that, generally,
this embodiment of the invention is less efficient than the
embodiment which uses non-information bearing signals in a first,
targeting, phase to reduce the number of vehicles in a second,
identification, phase.
[0143] Yet a further consideration relates to the possibility that
the highest priority participant may not be targeted in phase one
owing to a malfunction. Thus, for example, his indication signal
may not be received, having been obstructed by an obstacle in his
path or his signal is subject to fade. This may not matter if other
participants having the same priority have nevertheless been able
to transmit indication signals, since if the indication time slot
having the highest priority is determined and all the participants
associated therewith are targeted, even a participant whose
indication signal was lost will still be targeted. However, if a
sole participant's indication signal is lost this could prevent
correct determination of the highest priority participant.
[0144] The protocol can take this possibility into account by
reserving, preferably, the first indication time slot in the next
iteration for exclusive transmission therein by a non-targeted
participant having a higher priority than that of the targeted
participants. The control center then transmits a call message
inviting the targeted participants to transmit a respective
indication signal during any one of the indication slots except the
reserved indication slot.
[0145] So far as newly targeted participants are concerned, the
process is essentially unchanged; each of the newly targeted
participants transmits an indication signal during one of the
unreserved indication slots according to his respective priority.
However, any previously non-targeted participant having a higher
priority than that of the newly targeted participants transmits a
respective indication signal during the reserved slot. This slot is
referred to herein as an "Inter-Iteration Miss/Trap Control
Slot."
[0146] In a further preferred embodiment of the present invention,
at least one iteration of the targeting phase includes a control
slot, which is reserved for simultaneous transmission by all the
priority-bearing participants of the iterative stage responding to
the call sent from the control center. According to this preferred
embodiment, each priority-bearing participant transmits twice, once
during its characteristic-indicating slot as described above and
once during the control time slot. This control slot is referred to
herein as an "Intra-Iteration Miss/False Control Slot." This
control slot provides an independent indication of transmission by
at least one participant in response to the control center call
which initiated the iteration.
[0147] The additional indication obtained from the Intra-Iteration
Miss/False Control Slot will generally economize on both the total
processing time and the total transmission time of the targeting
phase. For example, if no transmissions are received in this
control slot, it may be assumed that any transmissions received in
the characteristic-indicating slots are due to a false alarm error
and, thus, further processing and transmissions derived from the
last iteration are avoided. Similarly, in a "miss" error situation
in which no participants are targeted, a transmission received in
this control slot indicates a possible "miss" and the last
iteration is preferably repeated. Thus, the use of a control time
slot improves the reliability of the targeting phase.
[0148] It should be noted that for improved reliability of the
detection process at the control center receiver, the remote
station transmitter may perform a more sophisticated transmission
process that includes diversity techniques based on randomly
varying the amplitude and or the phase of the transmitted signal,
so that any correlation between transmitters will be reduced when
detecting a sequence of transmission slots.
[0149] To further improve the reliability of the targeting phase, a
preferred embodiment of the invention employs a majority voting
techniques in which an odd number of slots greater than one, for
example three slots, are assigned to each range of characteristic
values. According to this preferred embodiment, each participant of
a given characteristic value transmits an indicating transmission
during each of the time slots assigned to the range. The given
characteristic value is taken into account only when indicating
transmissions are received in a majority of the slots assigned to
the value, for example by two slots out of three. When indicating
transmissions are received only by a minority of the slots assigned
to the value, for example by one slot out of three, the response is
preferably ignored. It should be appreciated that the odd number of
slots assigned to the given range of characteristic values may be
distributed among slots that have minimum correlation.
[0150] It is appreciated, however, that such majority voting
schemes which improve the over-all reliability of phase one,
consume substantial transmission and processing time. Therefore,
such schemes are preferably applied selectively, in potentially
problematic situations. For example, majority voting may be
employed only after a predetermined number of previous false alarms
and/or "misses" have been detected using the control slot technique
described above or otherwise.
[0151] Within a single iteration of phase one, the assignment of
priorities to each participant may be performed in respect of a
different sub-set of selection criteria for at least some of the
participants. In effect, this permits different search strategies
to be executed each in respect of a respective indication slot. For
example, the first indication slot having the highest priority may
relate to all participants who are located within a radius of 10 m
from the customer without any further restriction; whilst the
second indication slot may relate to all participants who are
located within a radius of 25 m and who have been awaiting
instructions for more than 20 minutes. By this means Boolean OR
search or other search strategies can be performed in a single
iteration.
[0152] Furthermore, during each iteration the participants may
optionally assign themselves a priority having a magnitude outside
the priority scale so as not to be targeted by the initiator. This
can be done if, for example, a participant is otherwise occupied or
for any other reason does not wish to receive instructions.
[0153] During a particular iteration the priorities assigned to
each participant are generally absolute with respect to a mutually
common scale which itself is external to the participants and
independent thereof. However, between successive iterations the
priority scale may well relate to different combinations of
selection criteria. By this means finely tuned search strategies
can be performed whereby all participants answering to a first
combination of selection criteria are targeted during a first
iteration, whilst all of the targeted participants answering to a
different combination of selection criteria are targeted during a
successive iteration.
[0154] Alternatively, the combination of criteria which make up the
priority may be information dependent and, for example, different
groups of slots may relate to different combinations of
criteria.
[0155] Once a sufficiently small number of participants are
targeted such that, in accordance with the protocol, identification
of a desired number of participants is likely to yield a successful
outcome, the second phase described above is commenced. The number
of identification slots to be allocated to the targeted
participants is calculated by first estimating the number of
targeted participants remaining at the end of phase one. The number
of identification slots is then calculated according to the
estimated number of targeted participants who must transmit
respective identification messages, so as to reduce the total time
required to identify the required number of participants.
[0156] In this connection, it will be realized that there exists a
tradeoff between allocating too many and too few identification
time slots. Specifically, allocating too many identification time
slots reduces the probability of a targeted participant selecting
an early identification slot, thereby increasing the time required
to identify the highest priority participants. On the other hand,
allocating too few identification time slots increases the
probability that more than one participant will select the same
identification time slot. In this case, the resulting collision of
more than one identification message makes it impossible to
identify the respective participants, requiring further iterations
and again increasing the identification time. In practice the
number of identification time slots may be minimized by increasing
the maximum priority resolution in phase one in order to target no
more than the expected number of participants who are to be
identified in phase two, or by using a random process to eliminate
some of the participants, such as that described above.
[0157] In the specific embodiments described above the process of
assigning priorities to each of the participants is performed
within the participating vehicles themselves since only they know
their locations relative to the customer. Moreover, the onus of
tracking the participants' movements in terms of their location,
availability, occupancy, loading and all the other selection
criteria which may be of significance is now passed to the
participating vehicles themselves as opposed to most hitherto
proposed systems wherein a central dispatcher had to keep track of
all these parameters.
[0158] As a result of the above, the communication channel between
the control center and the participants may be of relatively narrow
spectrum width compared with that of hitherto proposed systems.
Additionally, the task of targeting potentially suitable
participants is distributed amongst the participants themselves
rather than being determined solely by the control center. Such
distribution results in a reduction of computing power being
required by the control center.
[0159] While the selection criteria must obviously be known to the
participating vehicles, the manner in which this is made known can
be varied according to circumstances. Thus, for example, the
selection criteria may be fixed and known in advance to the
participants (in which case the selection criteria are not subject
to change). Alternatively, the selection criteria may be determined
on-line by the control center and then transmitted to all of the
participants together with the call message.
[0160] Thus, in the particular example described above, during the
first phase of targeting it may be predetermined that each sector
has a width of 10 km and that in subsequent phases, the width of
each remaining sector is reduced, for example, by a factor of 10
until the sector has a width of only 10 m, whereupon all those
vehicles within the 10 m width sector send an identification
message; or, alternatively, the width of each sector in each
respective phase of allocation may be transmitted to the
participants by the control center. In order to reduce the number
of participants in the identification phase, the resolution in the
targeting phase may be increased artificially, i.e., past the point
at which it is meaningful.
[0161] It should also be noted that once a particular participant
has been uniquely identified to perform a task, he is notified of
this in the normal way by the control center, in any one of a
number of ways which are well known in the art as for example, by
voice over a communication channel or by text or other data
transmission.
[0162] Furthermore, although in the preferred embodiment described
above, one participant is uniquely identified as the most suitable,
in fact it may sometimes be appropriate to omit the second phase of
identification altogether. In such cases, the participants having
the highest priority are not uniquely identified as individuals but
all are identified as a group. One such situation relates to an
improvement of service in particular areas. In this situation the
number of taxis in a given area is monitored and additional cars
are sent in to the area if there are not enough cars in the area.
The number of cars may be estimated statistically, for example,
from the number of slots having responses.
[0163] In a further preferred embodiment of the present invention,
the number of participants complying with given criteria is
estimated based on a down-sampling technique in which only a
portion of the complying participants actually respond to a call
from the control center. For example, the participants may be
assigned a given response probability such that only a given
percentage, for example ten percent, of the complying participants
respond to the call. Response time-slots are preferably randomly
selected by the different participants. If the number of response
slots is substantially greater than the number of responses, i.e.
the number of complying vehicles times the response probability,
the number of detected responses generally corresponds to the
number of responses which, in turn, is a down-sampled indication of
the number of complying participants.
[0164] Down-sampling is particularly useful for situations in which
the number of expected responses is high, such as for estimating
the number of vehicles in a given area, when very course selection
criteria are applied. On the one hand, in such a case the number of
responses is large enough to be statistically reliable, provided
that the number of responders is small enough compared to the
number of slots dedicated for this purpose. On the other hand, the
smaller number of participants transmitting simultaneously reduces
the total transmission power and, thus, prevents occasional bursts
of powerful transmission which may be in violation of FCC
co-channel interference or other regulations.
[0165] Another application of the system of priority assignment
according to the invention is in the assignment of available lines
for car-phones or transceivers. Presently, available lines are
allocated on a when available basis. Thus, one unlucky user may
wait a long time while a lucky user may get an immediate line. In a
preferred embodiment of the invention, when a user wants a line, he
indicates this either by pressing a call button or by lifting his
receiver. A computer chip associated with the car-phone notes the
time at which a line was requested.
[0166] Lines (communication channels) are allocated on a waiting
time basis. In operation, a control center broadcasts a call for
priorities in accordance with a targeting phase of the present
invention. The priority is assigned according to waiting time, and
the individual phones broadcast signals during time slots assigned
according to their waiting time or by some other special priority.
During a second identification phase one of the phones is
identified, in the same manner as described above, and is given the
available line.
[0167] Referring now to FIG. 8 there is shown schematically the
principal features associated with the control center shown in FIG.
1. Thus, there is provided a transceiver and modem 50 coupled to an
antenna 51 for effecting bi-directional communication with the
participants (taxis) and being connected to a message processor 53
which is coupled to a computer 54. Message processor 53 receives
non-demodulated signals from the transceiver and determines which
slots contain signals for the targeting phase and identifies the
participant(s) in the identification phase. A preferred embodiment
of such a receiver is shown in FIG. 15.
[0168] A service request is effected by customer 25 by telephoning
his nearest taxi rank and then dialing his telephone number, the
request being routed to the computer 54 via a Public Switched
Telephone Network (PSTN). The computer 54 converts the customer's
telephone number to a corresponding location based on a data base
stored in the computer. Alternatively, such communication can be
effected via an operator. A terminal 56 is coupled to the computer
54 for allowing an operator to enter commands and display data. In
addition the system also allows for voice signaling to a dispatcher
at the control station or for voice communication between the taxi
driver to the customer.
[0169] FIG. 9 shows the principal components associated with a
participant allocation unit 60 located in each of the vehicles.
Allocation unit 60 preferably includes a transceiver 61 coupled to
an antenna 62 for effecting bi-directional communication with the
transceiver 50 in the control center 37. Transceiver 61 is
connected to a vehicle computer 64 coupled to a microphone/handset
65 providing a human interface between the vehicle computer 64 and
the corresponding taxi driver.
[0170] A Global Positioning System 66 (GPS) or other position
determining system as known in the art receives positioning data
via an antenna 68. The Global Positioning System 66 is coupled to
the vehicle computer 64 and functions as a positioning means for
providing positioning information relative to a predetermined
origin in respect of the corresponding participant. Thus, once the
location of the customer is provided to the vehicle computer 64,
the latter, being coupled to the Global Positioning System 66 is
able to determine the relative location of the participant to the
customer and thus determine the participant's priority.
[0171] Associated with the vehicle computer 64 is a storage means
70 for storing the protocol according to which priorities are
assigned. Also stored in the storage means 70 are any singular
areas which can affect the actual route e.g. obstructions such as
rivers, road blocks and so on which result in the actual route
distance being longer than it would otherwise be. As explained
above, the handset 65 allows the driver to assign himself a
priority outside the range of the priority scale and, by such
means, to exclude himself from the process of targeting. It also
includes a microphone for establishing voice contact with the
control center, as well as paging means for obtaining a text
message therefrom.
[0172] The system described above may include a full duplex
broadcast network such that the control center does not need to
await responses from all of the participants before targeting the
highest priority participants. Thus, specifically, as soon as a
valid response is received by the control center, the participants
corresponding to the response can immediately be targeted or
identified whilst informing other participants to stop transmitting
indication signals or identification messages. This permits the
steps of targeting and/or identifying participants to be effected
more quickly. However, the invention may also be employed in a
simplex (i.e. half-duplex) broadcast network, albeit at the expense
of longer targeting and identification times since the control
center cannot transmit to the participants until all their
responses have first been received and validated.
[0173] It will be appreciated that, instead of employing a Global
Positioning System, other systems for determining a participant's
location can equally well be employed. For example, a route
scheduler based on dead reckoning responsive to each participant's
location can be used for determining a route having minimum
distance. Such a route scheduler might possibly comprise sensors
located at intervals along the road for sensing a passing vehicle's
presence and for transmitting to the vehicle data representative of
its location relative to a specified location for error correction.
Typically, such a route scheduler has a memory for storing therein
a scaled contour map so that an optimal route can be determined
taking into consideration the nature of the terrain. Likewise,
prevailing traffic conditions can be fed into the route scheduler
at regular intervals of time, so that traffic jams, roadwork and so
on can be considered when determining the optimal route.
[0174] In the foregoing description it has also been assumed that a
single channel broadcast network is employed. However, this is by
no means essential and a centralized controlled trunking system
having at least two channels may equally well be employed. This
permits more than one task to be handled simultaneously each on a
different broadcast channel. Thus, in the case of a two channel
broadcast network, for example, having first and second channels,
each call message is transmitted via a broadcast control channel so
as to be received by all the participants associated with the first
channel. Upon determining that he has not been targeted by the
control center, a participant starts to measure elapsed time and
waits a predetermined elapsed time locked on to the first channel
and thereafter returns to the broadcast control channel for
receiving further call messages.
[0175] The period of time during which a non-targeted participant
remains locked on to the first channel is of sufficient duration to
allow an updated priority to be assigned to the participant. Owing
to the dynamic variation in a participant's status, it may occur
that, with an updated priority, a previously non-targeted
participant becomes targeted in the next iteration. Thus, the
period of time during which a non-targeted participant remains
locked on to the first channel must further be of sufficient
duration to allow a corresponding indication signal and/or
identification message to be transmitted by the participant to the
control center, whereby the control center may target and/or
identify the participant.
[0176] Alternatively, the call message may be transmitted via a
broadcast control channel so as to be received by all the
participants associated with the first channel and, upon
determining that he has not been targeted by the control center, a
participant receives from the control center an instruction to
return immediately to the broadcast control channel. This
immediately frees a non-targeted participant to participate in a
subsequent search strategy on the second channel relating to a
different task.
[0177] According to yet another variation, an initial call message
is transmitted together with the selection criteria via a broadcast
control channel so as to be received by all the participants
associated with the first channel. Each of the participants
receiving the call message assigns to himself from the priority
scale a respective priority representative of his relative
suitability in accordance with the selection criteria and transmits
an indication signal during a respective indication slot. Only the
targeted participants remain switched to the first channel and
subsequent call messages are transmitted only to those participants
who have been previously targeted by the control center. This again
frees a non-targeted participant to participate in a subsequent
search strategy on the second channel relating to a different
task.
[0178] It will be appreciated that whilst the invention has been
described with particular application to a taxi dispatching
service, the invention has more general application wherever one or
a group amongst a plurality of participants is to be targeted in
accordance with their respective suitabilities based on at least
one selection criterion. It will further be understood that, whilst
the preferred embodiment has been described for the sake of
simplicity with regard to only two selection criterion (i.e.
distance and waiting time), in practice a large number of selection
criteria may be employed, all having different relative weights,
whereby an integrated search strategy may be implemented.
[0179] It will also be understood that whilst the invention has
been described with particular reference to 2 dimensional terrain,
it can equally well be applied in 3 dimensional space and is thus
suitable for air or space travel, as well as land and sea.
[0180] Mention should also be made of the variable parameters in
association with which the protocol functions. These are generally
application dependent and typically are provided with default
values built into the protocol. Thus, if distance is one of the
selection criteria, this fact may be represented by a default value
of an associated parameter. Likewise, the lower and upper bounds of
the priority scale and the priority resolution associated with each
iteration in phase one can been assigned to respective parameters
each having corresponding default values.
[0181] Any unassigned parameters must, of course, have values
assigned thereto prior to initiation of phase one. This can be done
during the initiation of the process prior to transmitting the
first call message to the participants. However, in certain
applications, all the parameters may have pre-assigned default
values which are acceptable for the application. In this case, the
call message merely starts the process enabling the participants to
determine the appropriate priority scale and assign themselves
respective priorities at the appropriate priority resolution; there
being no need to inform any of the participants of the boundary
values of the priority scale or of the priority resolution or
indeed of the selection criteria.
[0182] While the invention has been described with particular
reference to a wireless broadcast network, it will be appreciated
that the invention is capable of much more general application. For
example, hard-wired communication systems may also employ the
principles of the invention in which case the indication signals
need no longer be CW. In such cases the dynamic variables would
generally not be position; however the system is generally
applicable to systems with any set of dynamic variables.
[0183] The principles of the invention may also be used in a
routing system, for example to a system which identifies buses or
other vehicles which are delayed and adjusts the speed and/or
location of other buses to compensate therefor. In the first
(targeting) stage of this utilization of the invention, the
priority would for example be based on the amount of time that a
vehicle is behind schedule. Vehicles which are behind schedule more
than a predetermined amount would then be targeted and identified
in a second (identification) stage. Preferably, the identified bus
would then be asked for its exact position. Due to the fixed lineal
nature of bus routes, the position of the bus on the route is a one
dimensional function, i.e., the distance along the path.
[0184] A query would then be sent to other busses on the same bus
line asking them for their positions and, optionally, where they
stand in relation to their schedule. Based on this information, a
control center would determine corrective action to provide
improved service, which may include steps such as speeding up some
buses, as for example by operating them in a skip-stop fashion,
slowing some buses down, keeping some buses from leaving the
terminal or adding new buses to the route, perhaps at some
intermediate point on the route. Some indication of occupancy of
the buses would help to avoid sending full or almost full busses to
load additional passengers when less full buses are available. Such
indication, which could, for example, be keyed in by the bus
driver, would help in optimizing routing decisions. Suitable
instructions would, of course, be transmitted to these busses after
a corrective action plan is formulated.
[0185] Alternatively, information on deviations from schedule are
ignored, and a revised schedule is based only on the position of
the buses and optionally on their occupancy.
[0186] The principles of the invention are also applicable to a
routing system for determining slow areas of traffic and rerouting
traffic around such areas. In such a system a large number of
participating vehicles are queried as to the delays they are
experiencing, and the delay time is one example of a
"characteristic value" for the first phase of this embodiment. When
a vehicle experiences a delay above a threshold, the position of
the vehicle is determined in the second phase. It should be noted
that no identification signal per se is transmitted in the second
phase, instead a position signal is broadcast. Preferably, the
delay is also verified by the driver of the vehicle to avoid false
alarms.
[0187] Once the position of the targeted delayed vehicle is
determined, a new first (targeting) stage determines those vehicles
that are close to the specific delayed vehicle, and determines, by
successive second stages, the extent of the delay as a function of
the time of the delay. Furthermore, by making multiple queries, the
traffic conditions can be estimated. Based on this information, the
seriousness of the delay may be determined and corrective action,
such as re-routing of other vehicles, may be started. In
particular, information on the traffic conditions and the
geographical extent of the delay may be transmitted to vehicles
which have routing apparatus of types which are known in the art,
to be used by these apparatus for determining the optimum route for
the receiving vehicle.
[0188] In an alternative preferred embodiment of the invention, the
first query requests responses only from vehicles which are
experiencing delays greater than a given time (or which are moving
at an average velocity of less than a given velocity). Those
vehicles which meet the criteria then broadcast a signal in a time
or time/frequency or frequency slot which is indicative of the
absolute position of the vehicle. As in some of the previous
embodiments of the invention, it is expected that more than one
vehicle will broadcast in a particular slot and the system is
interested, at least at this stage, only in determining if there
are vehicles which are experiencing delays of a given
magnitude.
[0189] FIG. 10 shows an initial map generated by such a method,
wherein the area represented by a pixel (slot) may, for example, be
of the order of 250 to 1000 meters square.
[0190] In a preferred embodiment of the invention, the system then
determines, based, inter alia, on the extent of the various
contiguous areas which shows positive responses, a smaller area or
areas for further study. Preferably, the system then broadcasts a
further query requesting those vehicles within the more restricted
area which have at least a given delay (which may be the same as or
different from that used in the first query) to broadcast in a
position slot using a finer resolution, for example, 100 to 250
meters. Based on the responses to this query a second map such as
that shown in FIG. 11 is generated. As can be seen from FIG. 11,
various branches of a road network radiating from an intersection,
designated as A-F in FIG. 11, can be identified. To improve the
usefulness of the display, a background map, such as a road map may
be displayed underlying the displays of any of FIGS. 10, 11 or
13.
[0191] In the event that additional information relating to the
delay is desired, further queries can be made. For example,
vehicles which are traveling toward the intersection can be
requested to broadcast in a slot which corresponds to the slot they
are in and to their velocity toward the intersection. This allows
for generation of the graph shown in the lower portion of FIG. 12.
Additional slots may be used for the generation of other
information regarding the responding stations. Such information may
also be graphed as shown in the upper portion of FIG. 12.
[0192] Alternatively or additionally, a map which shows the average
velocity of the vehicles toward the intersection as a function of
the position can be generated. Such a map is shown in FIG. 13. To
acquire the information needed for generating such a map, a number
of queries may be made, each requesting an indication from all
vehicles within the area of interest having a given average
velocity toward the intersection. The responding vehicles would
broadcast their indication signals in slots corresponding to their
position. In the map of FIG. 13 the velocity for a given pixel is
determined, for example, as the average velocity of the reporting
slots for that position. In a display of the map of FIG. 13, the
velocity toward the intersection can, for example, be displayed as
a gray scale value or as a color, with for example red being the
highest delay and blue being a minimum displayed delay.
[0193] FIG. 14, which is a generalized block diagram for a system
useful for performing the IVHS function described above, shows a
base station or control center 91 having a control center
transmitter 79 which broadcasts queries and optionally other
signals to vehicles on command from a control computer 80. A remote
vehicle 85 (only one vehicle is shown for simplicity) receives the
query at a vehicle receiver 84 and transmits commands to a
microprocessor 86, based on the queries it receives from the
control center.
[0194] Microprocessor 86 also receives information regarding the
status of the vehicle from one or more information generators and
sensors indicated by reference numeral 88. This information may be
sent by the sensors on a regular basis or may be sent on command
from the microprocessor.
[0195] Microprocessor 86 is then operative to command vehicle
transmitter 90 to transmit indication signals (or if required
information bearing signals) in a suitable slot in accordance with
the information received by microprocessor 86.
[0196] The indication (or other) signals are received by a control
center receiver 92 and processed by receiver 92 and computer 80.
While the operation and construction of the apparatus designated by
reference numerals 82, 84, 86 and 90 is straightforward and needs
no further explanation, the operation of receiver 92 is usefully
expanded upon with reference to FIG. 15.
[0197] The system described above is based on a central decision
maker which receives information from vehicles, plans the routing
for each vehicle and then broadcasts a route or route changes to
the individual vehicles. This type of system has the advantage that
the routing for each vehicle takes account of the routing for the
other vehicles and the control center in computing the routings can
balance the routings to cause minimum delays. The disadvantage of
such a system is the large bandwidth required to notify the
individual vehicles of their individual corrected routes.
[0198] A second approach for routing systems which has been
suggested is to have each of the vehicles compute its own route,
based on some information about the present status of traffic which
it receives from a central transmitter. While such systems require
only a limited bandwidth, the routes computed by the individual
stations cannot take into account the future effects of the routes
of other vehicles.
[0199] In a preferred embodiment of the invention, vehicles compute
their own routing and then report, in response to a query, their
expected time of arrival at locations that are known to have a high
incidence of traffic jams and slowdowns (and preferably also
additional locations which do in fact have such slowdowns).
Preferably, such reporting is performed using the slot method of
transmission which does not identify the individual vehicles. Since
a large number of vehicles is involved, down-sampling as described
below may be effectively used to estimate the numbers of vehicles
which pass the locations.
[0200] Additionally or alternatively, the future development of
existing slowdowns can be estimated from the prior development of
the slowdowns, the rate of change of the length of the slowdown and
the average speed of the vehicles which are within the slowdown.
Such information can be made available to the vehicles based on
comparison of the development of slowdowns which are detected by
the methods which have been previously described above.
[0201] Based on the estimates of the numbers of and times of
arrival of the vehicles at the trouble spots, information on future
expected traffic jams is generated by the central station and
broadcast to the vehicles which update and recalculate their
individual routings. This recalculation of routs, broadcast of
times of arrival at trouble spots and estimations of future traffic
jams and slowdowns gives each vehicle the information required to
make a distributed system effective in avoiding future problems,
without the huge bandwidth requirements of central calculation of
the routes for the vehicles.
[0202] Such a distributed method may be applied to fleet management
and other systems.
[0203] For example, in a preferred embodiment of the invention, the
redistribution of a a fleet of taxicabs from a, present, actual
distribution to a desired redistribution is accomplished by having
the taxicabs choose, based on a predetermined algorithm and
information transmitted to them by a central station, which
taxicabs will move to a new location. In this redistribution
procedure, a present distribution (containing numbers of taxicabs
in a region, without necessarily any indication of the position of
individual identifiable taxicabs) and a new desired distribution is
transmitted to all of the taxicabs. Based on a predetermined
protocol, each of the taxis will decide locally if they are to move
to a new location. Preferably, a decision by each taxi is based on
a statistical model whereby generally approximately the correct
number of taxis decide, on their own, to move to new sites. This
protocol may consider parameters such as the location, idle time
and distance of individual taxi from the area which need additional
taxis, as well as the present distribution of taxis and what,
statistically, they will choose to do, based on the protocol.
[0204] Another similar application of the invention is bus fleet
management, where bus distribution information, occupancy
information, connection times, location distributions, etc., is
broadcast to the bus fleet to enable the buses to make distributed
decisions. In particular, based on the information received, a bus
may, in effect, instruct itself to skip a bus stop, wait (or not
wait) for a connection with another bus, to leave a starting point
early (or late), etc.
[0205] Generally speaking, the RF signals transmitted by the
vehicle may be at any frequency slot. It is to be expected (both
for the IVHS application and for the dispatching application
described above) that there will a certain amount of frequency
diversity caused by the imperfect accuracy and stability of the
vehicle transmitters 90. The slots are wide enough to accommodate
this diversity.
[0206] Furthermore, often the system utilizes very large numbers of
vehicles. If too many of these vehicles (in some particular
situation) transmit in the same slot, then the total power
transmitted may exceed authorized ERP or dynamic range
restrictions. To overcome this problem longer, lower power, pulses
may be used for indication signals. Furthermore, if a single
receiver is used for receiving signals for all of the slots,
intermodulation effects may cause spurious signals to appear in
slots for which no actual signals have been received.
[0207] These problems as well as near-end to far-end transmission
problems are substantially solved by the system shown in FIG. 15
and by certain constraints placed on the system which are not shown
in FIG. 15.
[0208] With respect to excess power problems, if it is expected
that many vehicles may transmit in a particular slot, the queries
can be designed so that fewer than the total number of vehicles
will respond, whenever this is possible. This can be accomplished,
for example by having the vehicles choose, statistically, which
vehicles will respond within a given percentage of the total number
of vehicles. The power transmitted by the vehicles can be adjusted
to a minimum based on either the known distance between the vehicle
and the control receiver, with each vehicle transmitting just
enough power so that detection of the signal by the control station
is assured. A further or alternative power adjustment may be made
by the vehicle transmitter based on the power received from the
control station, for example, during the query. Finally, a closed
loop system in which the query includes instructions as to the
power levels to be used may be used. It is not desired that such
closed loop system result in exactly the same power level being
received from each remote station be perfect since this would
increase the probability of amplitude correlation between the
signals and resultant destructive interference, usually in a
situation where a strong line of sight transmission exists between
a few vehicles and the base station. A balance should be struck
between a reduced variation in the power level received by the
control center from the various remote vehicles and keeping the
chances of destructive interference low.
[0209] Increased pulse duration can also reduce the transmitted
power for a given ratio of detection probability to false alarm
probability especially in the receiver shown in FIG. 15 and
described below.
[0210] Preferably, the amplitude of the signals broadcast during
the time slot is shaped over the broadcast period to reduce the
side-lobes of the signals and avoid false signals in adjacent
frequency slots, which may be a problem when large numbers of
vehicles broadcast at the same time. Alternatively or additionally,
frequency windowing at the receiver may be used to reduce
cross-talk between channels.
[0211] Dynamic range limitations can be reduced by providing
multiple receivers, each covering only a portion of the frequency
band. Finally the novel receiver of FIG. 15 may be used to
determine the presence or absence of signals in particular
slots.
[0212] FIG. 15 shows a receiver system corresponding generally to
reference number 92 and to a portion of computer 80 of FIG. 14. In
general such a receiver is also useful for the first phase of the
dispatching system described above as well as for the IVHS
system.
[0213] An antenna 94 (or an array of antennas) receives signals
from a plurality of vehicles simultaneously and passes them to
receiver and (optionally) AGC 96. Receiver and AGC 96, which may be
of conventional design, downconverts the received signals from RF
to IF frequencies. The threshold levels of the detection process
may be dependent on the AGC process. The IF signal is digitized by
an A/D system 98 and further down converted by a downconverter 100
to base band. It should be understood that this
receiver/downconverter system does not demodulate the incoming
signals, but only downconverts the RF so that the same relative
frequency differences of the signals is present at the output of
convertor 100 as in the incoming signals, except that the absolute
frequency has been reduced to a low frequency from the RF frequency
of the transmitted signal. At these lower frequencies digital
systems can be used to analyze and detect the signals.
[0214] The low frequency band signals are fed to a series of
correlation filters 102 (correlation-type receiver), each of which
has a very narrow bandwidth which is related to the correlation
time of the correlation filter. Preferably, the frequency
bandwidths of adjacent receivers 102 overlap so that the entire
bandwidth of each of the slots is covered by one set of receivers
102. The output of each of the receivers is compared to a threshold
104 to determine if a signal is present at the frequency of the
respective receiver 102 and the outputs of all of threshold
detectors for a given slot are OR gated to determine if any signal
is present in the slot. Alternatively, the outputs of the
correlation receivers can be summed and this sum signal used to
determine if any signal is present in the slot. However, this will
generally result in increased noise.
[0215] In an alternative preferred embodiment of the invention, the
strongest output of the set of correlation receivers is chosen for
comparison with a threshold, with or without post-detection
integration.
[0216] Use of a plurality of overlapping narrow band receivers in
this manner also reduces the extent of side lobes of the detection
process outside the band of the slot. This allows for closer
frequency spacing of the slots since interference between slots
having adjacent frequencies is reduced.
[0217] One set of receivers 102, threshold detectors 104 and an OR
gate is provided for each slot and is referred to herein as a slot
detector unit. Slot detector units for all of the slots feed a data
processor 108 which, together with computer 80 processes the data
as described above. When large numbers of vehicles are used in the
system and intermodulation becomes a problem (or if AGC is used,
and low level signals are lost), it may be necessary to provide a
plurality of front end portions of receiver 92 (the front end being
defined as receiver 96, convertor 98 and converter 100), where each
front end receives signals from only a portion of the entire
frequency band including one or many of the slots. The function of
correlation receivers 102 may also be implemented, for example,
using set of DFTs or an FFT (for CW signals), matched filters or
other correlation receiver methods or other optimum receiver
methods, depending on the transmitted signals. Other methods such
as energy detectors (e.g., radiometers) with or without tracking
may also be used, however, they will give less optimal results,
because of practical limitations on input band-pass filter
designs.
[0218] It should be understood that using a plurality of
correlation receivers for the same slot may increase the false
alarm probability and hence the threshold for positive detection
may be adjusted to provide a desired low false alarm
probability.
[0219] For all the above applications of the invention, destructive
signal interference between units which broadcast in the same slot
can be further reduced by performing transmission diversity
operations such as random phase (for example, 180.degree. and
0.degree.) and/or amplitude changes, at the transmitters of the
remote stations.
[0220] Additionally or alternatively, the effect of interference
from large signals on small nearby signals can be reduced by
performing detection in a two step process. In the first step, only
slots having signals having a value above a given level are
validated. This level can be fixed in advance or can be adaptive,
depending on the signal levels actually detected. If none of the
signals are high enough to cause concern that they have caused
signals to occur in other slots then, preferably, there is no need
for the second step and all signals above a baseline level are
validated.
[0221] If the two step detection process is chosen, then all
stations, except those broadcasting at the validated slots are
asked to broadcast again. This will avoid spillover into other
slots and the smaller signals can then be properly received without
interference. It may be necessary in some cases to repeat this
process additional times if very large signal variations are
expected.
[0222] In a preferred embodiment of the invention, an improved
probability of detection may be desired for some of the slots, such
as, for example, the control slots. For these slots repeated
transmission of signals using transmission diversity may be
performed and detection enhancement methods such as post detection
integration may be used to improve the detection probability.
[0223] The system may also be provided with a display 110 for
displaying the data, such as the maps and graphs of FIGS. 10-13 and
with a user interface 112 which is used by an operator to control
both the operation of the system. The user interface also
preferably controls the display and the memory to allow for the
operator to review the maps previously generated or to generated
new displays based on information previously received.
[0224] Information may be sent by the control center to the
vehicles to enable them to minimize average travel delays. This
information may consist of the above mentioned maps or of travel
delay information at various intersections. The vehicles can then
use this information to optimize their route. Alternatively, the
control center may send routing information to some of the vehicles
in order to equalize traffic delays. In either event, the fast
response of the system in a matter of seconds allows for real time
supervision, adjustment and continuous stabilization of traffic
patterns with additional iterations. As described above, in a
distributed system only prospective traffic patterns is broadcast
by the control center and each vehicle calculates its own
route.
[0225] The IVHS system described above is also useful in tracking
situations such as for fleet management.
[0226] In a further preferred embodiment of the invention the
position and other characteristics of a large number of vehicles
can be mapped and tracked in near real time using a relatively
narrow bandwidth. In this embodiment each vehicle is assigned a
number of slots, which are used only by that vehicle, according to
a predetermined protocol.
[0227] The vehicles are preferably first mapped with a preferred
mapping phase of a mapping and tracking procedure. A way to perform
this phase is to devote a small matrix to each vehicle to be
tracked. This smaller matrix is part of the entire matrix of slots
assigned by the control center. The smaller matrix represents, for
example, (in mapping of spatial coordinates) a square area which is
divided into nine sub-areas, each of the sub-areas represented by
one of nine slots assigned to a particular vehicle. In a first
iteration a large area is divided into nine sub-areas and a vehicle
broadcasts a signal in the slot which corresponds to its present
position. In a second step of the mapping phase, the area in which
the vehicle previously broadcast is expanded to fill the nine
slots, with a finer resolution. Alternatively, the area which is
zoomed into the nine slots is slightly larger than the area of the
previous broadcast to avoid a situation in which the vehicle was at
the border of the area and left the area between steps.
[0228] This identification of one sub-area and consequent
convergence to a higher resolution is repeated several times until
the required resolution is achieved. The highest practical
resolution, as will become clear below, is the distance that a
vehicle could travel in the time it takes to perform a tracking
cycle as described below. Within five iterations the individual
resolution can be improved from a 10 km square (divided into nine
3.3 km squares) to resolution of about a 40 meter square area.
[0229] It should be understood that while this aspect of the
invention is generally described with respect to a two dimensional
spatial matrix (north-south and east-west for example) the
invention is especially useful and efficient for tracking buses,
trains or other such moving remote stations which move along a line
(their route). In this very common situation, only one dimensional
positional information is required, the dimension being the
distance along the route.
[0230] In a second, tracking, phase of the mapping and tracking
procedure, performed periodically after the required resolution is
reached, nine slots, for example, representing a 3.times.3 area of
minimum resolution areas, are used to track additional movements of
the vehicle. In one embodiment of the invention the central one of
the nine areas corresponds to the area occupied by the vehicle at
the end of the mapping phase (or during a previous periodic
updating iteration of the tracking phase). During each periodic
update, each vehicle broadcasts in a slot which corresponds to
either its previous position (the slot corresponding to the center
area of the 3.times.3 group of areas) or one of the adjoining
areas. In the next iteration, the newly chosen area is the center
of the 3.times.3 matrix, according to a predetermined protocol.
[0231] For a one-dimensional tracking system, only three slots are
required, where one slot (conceptually the center slot) represents
the last previous position along the route and the other two slots
represent positions in the two directions along the route.
[0232] In a further preferred variation of this embodiment of the
invention, only 5 slots are utilized to map into the 3.times.3
area. One of these slots represents, as a reference, one of the
corner (or the center) areas of the 3.times.3 area and the other 4
slots represent north-south or east-west variations. In this the
vehicle may broadcast during one or two of the five slots,
depending on the deviation, if any, from the corner (or center)
area chosen as reference. If the vehicle is in the reference area,
broadcasting takes place only in the slot which represents the
reference area. If the vehicle is in the areas north-south-east or
west of the reference, then the vehicle broadcasts in only one slot
representing such deviation from the reference. If the vehicle
moves into an area diagonally shifted from the reference, the
vehicle will broadcast during two slots representing, for example,
the east-west and north-south deviations of the area in which the
vehicle is situated.
[0233] Similarly, only two slots would be needed for
one-dimensional mapping.
[0234] If a vehicle does not respond or its response was not
detected during a given iteration (i.e., if the vehicle is lost or
an erroneous code is received) a number of remedial steps are
possible. The particular vehicle (or some or all the vehicles) may
be requested to retransmit the particular iteration, or may be
asked to return to perform the previous iteration or a sequence of
previous iterations or to operate at a lower mapping resolution. In
some situations it may be desirable to start the process over, at
the lowest resolution for the particular vehicle or for all of the
vehicles, for example to repeat the entire process or some of the
steps of the process to increase reliability and to deduce the
extent of accumulated errors, even if no errors are detected. The
process may be repeated using the previous position information or
with present information with a lower resolution especially to find
"lost" vehicles.
[0235] FIG. 16B shows the slots in which a signal would be
broadcast in the tracking phase (or possibly in the mapping phase)
to indicate each of three positions of the vehicle shown in FIG.
16A, while FIG. 16C shows the slots which would be used if a corner
area were used as the reference. It should be noted that for either
case the vehicle was in the center area during the previous
tracking iteration.
[0236] While it appears from FIGS. 16A-16C that it is desirable to
have north south deviations represented by a change in slot
frequency and east west variations represented by a change in slot
time, it is actually more practical to use the same frequency for
all small matrix slots used by a particular vehicle, since this
requires only one transmitter per vehicle.
[0237] While it is desirable to dedicate particular transmission
slots for each vehicle, it is possible to have overlapping assigned
transmission slots. For example, if one slot for one vehicle is the
same as a slot for another vehicle, then if a signal is received in
the shared slot, the systems checks if a signal was received in one
of the unshared slots for one of the vehicles. If it was, then the
signal in the shared slot is considered as coming from the other
vehicle. If no signal is received in unshared slots for either
vehicle, then the signal is considered as coming from both
vehicles.
[0238] In a preferred embodiment of the invention, nine areas are
represented by a four bit word which is more than sufficient to
define the 3.times.3 matrix of elements. In this or similar cases
the "physical slots" described above may be represented by any
convenient code.
[0239] Furthermore, the logical slots may have different meanings
or resolutions in the same logical matrices. For example, the
position resolution of the logical elements may depend on the
maximum expected velocity of the vehicle and the resolution in the
two mapped directions need not be the same. Additionally, for
mapping and tracking along a road, one dimension may be the (one
dimensional) position along the length of the road and other
logical slots, if any, may, for example, represent the lane in
which the vehicle is traveling. Alternatively, as described above,
only one-dimensional tracking may be performed.
[0240] While according to one preferred embodiment of the
invention, as described in the previous paragraph, the spatial
resolution of the system is fixed and depend on the maximum
expected velocity of the system, this embodiment limits the number
of vehicles which can be tracked and/or the spatial resolution with
which they are tracked. For example, if the time between queries is
three seconds, the space resolution cannot be any finer than the
distance the vehicle would travel at maximum speed. If a particular
resolution is required for slow moving vehicles, then the number of
vehicles must be limited so that no vehicle, moving at its top
speed, would be outside the range of the 3.times.3 or 3.times.1
position matrix at this resolution when the next position query is
responded to.
[0241] In order to improve the trade-off between spatial resolution
and number of vehicles, the resolution of the system is adapted to
the current speed of the vehicle, in accordance with a preferred
embodiment of the invention.
[0242] In accordance with one particular embodiment, an additional
slot is associated with each vehicle. The vehicle transmits a
signal in this slot in accordance with its present velocity (or
distance traveled since the previous query) and an associated
resolution of the slot. Thus if the vehicle velocity (or distance
traveled) is greater than a given velocity (or distance), a signal
is broadcast in the additional slot. When such a signal is
broadcast, the resolution of the slots is decreased to accommodate
the higher velocity (or distance). When no such signal is
broadcast, the resolution is at the higher level.
[0243] In accordance with a second particular embodiment, no
additional slot is required for adaptive resolution. In addition,
the resolution may be varied in small discreet steps rather than
there being only two steps. In accordance with this embodiment, the
resolution represented by the slots depends on the prior history of
the vehicle. If, for example, if a vehicle broadcasts that it is
moving in a particular direction for more than a given number of
iterative queries of position, the supposition is that its speed is
increasing. For this situation the resolution of the system, for
that vehicle, is reduced, automatically, by increasing the distance
represented by each resolution element. For example, if a bus or
other unit broadcasts twice (or alternatively three times) in a row
in the slot representing movement out of the central slot in a
given direction, the resolution is decreased by a given percentage,
for example 10%-50%. If the situation continues, then the
resolution is decreased further, until the unit broadcasts, at
least some of the time, in the slot which represents the "central"
position. On the other hand, if the unit responds in the central
position more than a given number of times, then supposition is
that the speed is decreasing or that the unit is stopped. In this
situation the resolution is increased, in stages, until either the
unit broadcasts occasionally in the left of right positions or
until it reaches a maximum resolution.
[0244] It should be understood that since the unit does not
generally accelerate to high speed in a very short time, especially
from a stop, there is little or no chance that synchronization will
be lost, even if a very high resolution is used when the vehicle is
stopped or moving very slowly. The highest resolution may, in this
embodiment, be limited only by how far the vehicle can move from a
stopped condition, during the system cycle time. This is a much
higher resolution than the distance it can move at top speed which
is the highest resolution for the non-adaptive system.
[0245] In accordance with a third particular embodiment, a
4.times.4 or 4.times.1 matrix of positions is allocated, depending
on whether two or three dimensional mapping is required. In this
embodiment, the center of the position element which was previously
reported as containing the unit is translated, for the next
iteration, to reside at the center of the matrix, i.e., between
resolution elements. The distances represented by the slots is then
adjusted based on the history of position indications received from
the unit.
[0246] In accordance with a fourth particular embodiment of the
invention a 2.times.2 or 2.times.1 matrix is assigned for each
vehicle during the tracking stage. The central position represents
the center of the last previous reported position element as in the
third particular embodiment. In this system, the unit must report
"movement" to the left or right. However, this reporting actually
represents whether it is at the left or right of the center of the
last previous reporting element and may not represent actual
movements to the left or right or any actual movement at all.
[0247] If the vehicle reports that it has moved to the left during
the query time for two (or three) consecutive queries, then the
distance represented by each slot is increased, as described above.
When the resolution is consistent with the speed of the unit, the
unit will report alternate leftward and rightward "movements." It
should be understood that this reporting does not represent actual
leftward and rightward movements but rather movements greater than
or less than one half-resolution element.
[0248] If the resolution has been decreased as a result of movement
in one direction and the resolution has been adjusted to suit,
partially or fully, continued alternating leftward and rightward
reports may represent either continued movement at the same speed
or slowing down of the vehicle. Thus, the size of the resolution
element is reduced (the resolution is increased) until the
alternative direction reporting sequence no longer holds or until a
minimum resolution element is achieved. It should be understood,
that when the unit is stationary, the alternative reporting
situation will always result, so that an increase in resolution (to
the maximum available based on the acceleration of the unit) should
be attempted whenever the alternative direction reporting sequence
is achieved.
[0249] In accordance with a fifth particular embodiment, utilizing
the same logic as the fourth embodiment, only a single slot need be
assigned to each vehicle traveling along a route. In this fifth
embodiment the broadcasting of a signal within the slot or silence
indicates either the left or right logical slot of the fourth
particular embodiment.
[0250] Furthermore, if only forward movement is assumed, then at
least one less slot is required (except of course for the fifth
particular embodiment, since movement need only be reported in one
direction for each dimension.
[0251] In addition to tracking position, the above described
systems can be used to report additional variables. For example,
for buses, other slots may be used to provide other information
about the bus such as occupancy level. In such a situation after an
initialization phase similar to that for position, one slot may
represent no substantial change in the occupancy, with two other
slots representing an increased occupancy of the bus and another
slot representing a decreased occupancy. Such allocation allows for
occupancy to be tracked in a simple way, similar to the position
tracking described above, simultaneously with the position tracking
or at a lower frequency, interleaved with the position tracking
responses.
[0252] While the preceding mapping and tracking system implies that
each vehicle in the system is a priori included in the map, this is
not necessarily a requirement of the system. Each of these vehicles
would then be assigned slots for use in the mapping and/or tracking
phases. The vehicles from whom identification is requested may be
chosen in accordance with a criteria of the vehicle determined
according to any one of the procedures outlined above in which
vehicle having certain characteristics are determined.
[0253] In a mapping and/or tracking system according to the present
invention only a small number of bits must be transmitted for each
iteration. Using such a system can be especially worthwhile if the
transmission protocols and equipment are designed according to the
criteria described above with regard to the targeting and
identification and IVHS systems. In the present system, and for
systems having only several bits (such as up to 10 or a few tens of
bits) of information, it is useful to use a transmission protocol
without interleaving and FEC. Furthermore, protocols which require
a preamble including a substantial number of training pulses for
locking onto the frequency are also wasteful in view of the small
number of transmitted pulses. In a preferred transmission/receiving
system, the transmitted pulses are made long enough so that their
bandwidth is very narrow and are received by a system which is
capable of taking advantage of such a narrow bandwidth system
despite the inherent instability of the transmitters. Such a system
is described above with respect to FIG. 15.
[0254] Furthermore, the transmission power of such systems need not
be very high, even for transmission over relatively long distances,
because of the very high effective signal to noise ratio of the
receivers. Nor does the power have to be very constant over the
transmission, since the receiver is sensitive to the total energy
in the pulses and is not sensitive to the transient rise of the
transmitter. Thus, there is no need in the present system to wait
for the power in the transmission to rise to the design value as in
conventional systems. This combination of factors allows for
transmission to begin almost immediately, without considering the
attack, or rise time of the transmitter.
[0255] It may also be useful, in a preferred embodiment of the
invention, to provide diversity techniques, such as time and/or
frequency and/or microscopic space diversity techniques, as are
known in the art, to improve system reliability, especially in a
mobile communication environment.
[0256] Thus, while the pulse widths used in the present system may
be several times longer than those used in standard digital
transmission systems, the lack of overhead caused by the absence of
locking preambles, wait for transmitter power attack time and error
correction more than makes up for the longer pulse times, for
relatively small numbers of bits per transmission. The exact design
of a system depends on many factors such as distance, power
available, resolution required, available bandwidth, etc. However,
it has been found that, in general, the present invention provides
a much higher capability for mapping and tracking than conventional
systems.
[0257] In general, one or more base stations may be used for
broadcasting calls and/or receiving responses from remote stations.
If more than one base station is used, each station preferably
performs a reduction of the data which it receives by either
choosing its best candidate for performing the task or by
performing a mapping function of its nearby region or of its
associated vehicles. The base stations then preferably send this
reduced information to a central base station which makes the final
decision, constructs the desired map or performs any other final
analysis. Furthermore, the central base station would, in a
preferred embodiment of the invention, instruct each of the base
stations as to which additional queries they should make. In this
situation the subsequent queries need not be the same for all the
base stations.
[0258] In addition, in a preferred embodiment of the systems of the
invention, the base station broadcasts the information which it has
received from all the stations. This information is preferably
broadcast on a separate conventional data transmission channel. The
signal is received by the remote stations and is used for error
correction by them and, preferably, to allow for improved
stabilization of a traffic situation or improved interaction
between the various remote vehicles as described above.
[0259] For large areas of coverage, the area may be serviced by a
plurality of base stations which are all available to receive
signals from all of the remote stations. This redundancy of base
station receivers allows for mapping and tracking over a larger
area than with a single base station. Furthermore, in a preferred
embodiment of the invention, the base stations are the preferential
receiver for those remote stations which are closest to it. In this
regard, transfer of a remote station from one preferential base
station to another is automatic since it can be made based on the
previous map of the positions of the remote stations. Such
preferential assignment of the remote stations to a base station
may be accomplished without any action by the remote station such
as a change in slot allocation and the chances of losing
synchronization with the remote station, as often occurs with
cellular systems, is minimized.
[0260] While the preferred base station is the primary receiver of
signals from "its" remote stations, signals received from other
base stations may also be used. If such signals are used, the
weight given to them may depend on the position of the remote
station. This may be considered an advanced form of macroscopic
diversity.
[0261] In a preferred embodiment of the invention, the targeting
and preferably the identification protocols described above may be
performed in conjunction with the mapping and tracking protocols of
the present invention. In this way a subset of remote stations
whose movement or other characteristic values are of interest are
first targeted, preferably identified and then mapped and cracked
in accordance with mapping and targeting protocols. It may be
desirable to assign particular slots to the identified units prior
to the mapping and tracking sequences.
[0262] If the targeting criterion is the same as the criteria to be
tracked (for example position), then the mapping stage may begin at
the resolution range utilized in the targeting phase, or omitted
altogether.
[0263] In a further preferred embodiment of the invention, a pager
system having an appointment making capability operates on
principles similar to those described above. For example, the pager
system may broadcast a request to one or more pagers which also
incorporate an appointment calendar. The individual pagers
broadcast a signal in one or more of a matrix of slots which
correspond to busy times. The appointment may then be made for
other times. The individuals are then notified, by pager, that an
appointment has been made for them.
[0264] In many of the above embodiments of the invention, the
system is triggered and/or synchronized according to a synch signal
broadcast by the control station. Other sources of synchronization,
which synchronize both the remote and control station, such as GPS
received signals or other timing signals, can be used to trigger
and/or synchronize the system.
[0265] Reference is made to PCT application PCT/EP95/01330, the
disclosure of which is incorporated herein by reference, and
especially to an analysis of the communication resources required
by some of the embodiments of the above described inventive
apparatus and method compared to polling. This analysis may be
useful in giving a better understanding of the reasons for the
improved performance of the present invention.
[0266] The invention has been described herein using examples in
which the indication signals are transmitted in time, frequency or
time and frequency slots. Other types of transmission slots are
also useful in the invention such as frequency hopping and other
spread-spectrum transmission slots. The term "transmission slots"
or "slots" as used herein includes all these types of slots.
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